[PATCH next v3 00/15] printk: remove logbuf_lock

[PATCH next v3 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v3 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v2 is here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types, and a
new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. Since this
involved touching all the kmsg_dump users, we also decided [1] to
use this opportunity to clean up and clarify the kmsg_dump semantics
in general.

This series is based on next-20210225.

Changes since v2:

- use get_maintainer.pl to get the full list of developers that
  should at least see the changes in their respective areas

- do not disable interrupts in arch/um kmsg_dumper (because there is
  no need to)

- protect the mtd/mtdoops kmsg_dumper buffer against concurrent
  dumps

- update kerneldoc for kmsg_dump_get_line() (@len_out)

- remove ksmg_dump's @active flag

- change kmsg_dumper callback to:
  void (*dump)(enum kmsg_dump_reason reason);

- rename kmsg_dumper_iter to kmsg_dump_iter

- update kmsg_dumpers to use their own kmsg_dump_iter (and
  initialize it with kmsg_dump_rewind() if necessary)

John Ogness

[0] https://lkml.kernel.org/r/20210218081817.28849-1-john.ogness@linutronix.de
[1] https://lkml.kernel.org/r/YDeZAA08NKCHa4s%2F@alley

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX for improved multi-line support
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c             |  14 +-
 arch/powerpc/platforms/powernv/opal-kmsg.c |   3 +-
 arch/powerpc/xmon/xmon.c                   |   6 +-
 arch/um/kernel/kmsg_dump.c                 |  15 +-
 drivers/hv/vmbus_drv.c                     |   7 +-
 drivers/mtd/mtdoops.c                      |  20 +-
 fs/pstore/platform.c                       |   8 +-
 include/linux/kmsg_dump.h                  |  49 +--
 kernel/debug/kdb/kdb_main.c                |  10 +-
 kernel/printk/internal.h                   |   4 +-
 kernel/printk/printk.c                     | 456 ++++++++++-----------
 kernel/printk/printk_safe.c                |  27 +-
 12 files changed, 309 insertions(+), 310 deletions(-)

-- 
2.20.1

[PATCH next v3 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v3 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v2 is here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types, and a
new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. Since this
involved touching all the kmsg_dump users, we also decided [1] to
use this opportunity to clean up and clarify the kmsg_dump semantics
in general.

This series is based on next-20210225.

Changes since v2:

- use get_maintainer.pl to get the full list of developers that
  should at least see the changes in their respective areas

- do not disable interrupts in arch/um kmsg_dumper (because there is
  no need to)

- protect the mtd/mtdoops kmsg_dumper buffer against concurrent
  dumps

- update kerneldoc for kmsg_dump_get_line() (@len_out)

- remove ksmg_dump's @active flag

- change kmsg_dumper callback to:
  void (*dump)(enum kmsg_dump_reason reason);

- rename kmsg_dumper_iter to kmsg_dump_iter

- update kmsg_dumpers to use their own kmsg_dump_iter (and
  initialize it with kmsg_dump_rewind() if necessary)

John Ogness

[0] https://lkml.kernel.org/r/20210218081817.28849-1-john.ogness@linutronix.de
[1] https://lkml.kernel.org/r/YDeZAA08NKCHa4s%2F@alley

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX for improved multi-line support
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c             |  14 +-
 arch/powerpc/platforms/powernv/opal-kmsg.c |   3 +-
 arch/powerpc/xmon/xmon.c                   |   6 +-
 arch/um/kernel/kmsg_dump.c                 |  15 +-
 drivers/hv/vmbus_drv.c                     |   7 +-
 drivers/mtd/mtdoops.c                      |  20 +-
 fs/pstore/platform.c                       |   8 +-
 include/linux/kmsg_dump.h                  |  49 +--
 kernel/debug/kdb/kdb_main.c                |  10 +-
 kernel/printk/internal.h                   |   4 +-
 kernel/printk/printk.c                     | 456 ++++++++++-----------
 kernel/printk/printk_safe.c                |  27 +-
 12 files changed, 309 insertions(+), 310 deletions(-)

-- 
2.20.1

[PATCH next v3 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v3 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v2 is here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types, and a
new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. Since this
involved touching all the kmsg_dump users, we also decided [1] to
use this opportunity to clean up and clarify the kmsg_dump semantics
in general.

This series is based on next-20210225.

Changes since v2:

- use get_maintainer.pl to get the full list of developers that
  should at least see the changes in their respective areas

- do not disable interrupts in arch/um kmsg_dumper (because there is
  no need to)

- protect the mtd/mtdoops kmsg_dumper buffer against concurrent
  dumps

- update kerneldoc for kmsg_dump_get_line() (@len_out)

- remove ksmg_dump's @active flag

- change kmsg_dumper callback to:
  void (*dump)(enum kmsg_dump_reason reason);

- rename kmsg_dumper_iter to kmsg_dump_iter

- update kmsg_dumpers to use their own kmsg_dump_iter (and
  initialize it with kmsg_dump_rewind() if necessary)

John Ogness

[0] https://lkml.kernel.org/r/20210218081817.28849-1-john.ogness@linutronix.de
[1] https://lkml.kernel.org/r/YDeZAA08NKCHa4s%2F@alley

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX for improved multi-line support
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c             |  14 +-
 arch/powerpc/platforms/powernv/opal-kmsg.c |   3 +-
 arch/powerpc/xmon/xmon.c                   |   6 +-
 arch/um/kernel/kmsg_dump.c                 |  15 +-
 drivers/hv/vmbus_drv.c                     |   7 +-
 drivers/mtd/mtdoops.c                      |  20 +-
 fs/pstore/platform.c                       |   8 +-
 include/linux/kmsg_dump.h                  |  49 +--
 kernel/debug/kdb/kdb_main.c                |  10 +-
 kernel/printk/internal.h                   |   4 +-
 kernel/printk/printk.c                     | 456 ++++++++++-----------
 kernel/printk/printk_safe.c                |  27 +-
 12 files changed, 309 insertions(+), 310 deletions(-)

-- 
2.20.1


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

[PATCH next v3 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v3 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v2 is here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types, and a
new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. Since this
involved touching all the kmsg_dump users, we also decided [1] to
use this opportunity to clean up and clarify the kmsg_dump semantics
in general.

This series is based on next-20210225.

Changes since v2:

- use get_maintainer.pl to get the full list of developers that
  should at least see the changes in their respective areas

- do not disable interrupts in arch/um kmsg_dumper (because there is
  no need to)

- protect the mtd/mtdoops kmsg_dumper buffer against concurrent
  dumps

- update kerneldoc for kmsg_dump_get_line() (@len_out)

- remove ksmg_dump's @active flag

- change kmsg_dumper callback to:
  void (*dump)(enum kmsg_dump_reason reason);

- rename kmsg_dumper_iter to kmsg_dump_iter

- update kmsg_dumpers to use their own kmsg_dump_iter (and
  initialize it with kmsg_dump_rewind() if necessary)

John Ogness

[0] https://lkml.kernel.org/r/20210218081817.28849-1-john.ogness@linutronix.de
[1] https://lkml.kernel.org/r/YDeZAA08NKCHa4s%2F@alley

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX for improved multi-line support
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c             |  14 +-
 arch/powerpc/platforms/powernv/opal-kmsg.c |   3 +-
 arch/powerpc/xmon/xmon.c                   |   6 +-
 arch/um/kernel/kmsg_dump.c                 |  15 +-
 drivers/hv/vmbus_drv.c                     |   7 +-
 drivers/mtd/mtdoops.c                      |  20 +-
 fs/pstore/platform.c                       |   8 +-
 include/linux/kmsg_dump.h                  |  49 +--
 kernel/debug/kdb/kdb_main.c                |  10 +-
 kernel/printk/internal.h                   |   4 +-
 kernel/printk/printk.c                     | 456 ++++++++++-----------
 kernel/printk/printk_safe.c                |  27 +-
 12 files changed, 309 insertions(+), 310 deletions(-)

-- 
2.20.1


_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um

[PATCH next v3 01/15] um: synchronize kmsg_dumper

[John Ogness]

The kmsg_dumper can be called from any context and CPU, possibly
from multiple CPUs simultaneously. Since a static buffer is used
to retrieve the kernel logs, this buffer must be protected against
simultaneous dumping. Skip dumping if another context is already
dumping.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/um/kernel/kmsg_dump.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 6516ef1f8274..4869e2cc787c 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/string.h>
 #include <shared/init.h>
@@ -9,6 +10,7 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
 	size_t len = 0;
@@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (con)
 		return;
 
+	if (!spin_trylock(&lock))
+		return;
+
 	printf("kmsg_dump:\n");
 	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
+
+	spin_unlock(&lock);
 }
 
 static struct kmsg_dumper kmsg_dumper = {
-- 
2.20.1

[PATCH next v3 01/15] um: synchronize kmsg_dumper

[John Ogness]

The kmsg_dumper can be called from any context and CPU, possibly
from multiple CPUs simultaneously. Since a static buffer is used
to retrieve the kernel logs, this buffer must be protected against
simultaneous dumping. Skip dumping if another context is already
dumping.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/um/kernel/kmsg_dump.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 6516ef1f8274..4869e2cc787c 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/string.h>
 #include <shared/init.h>
@@ -9,6 +10,7 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
 	size_t len = 0;
@@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (con)
 		return;
 
+	if (!spin_trylock(&lock))
+		return;
+
 	printf("kmsg_dump:\n");
 	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
+
+	spin_unlock(&lock);
 }
 
 static struct kmsg_dumper kmsg_dumper = {
-- 
2.20.1


_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um

[PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[John Ogness]

The kmsg_dumper can be called from any context and CPU, possibly
from multiple CPUs simultaneously. Since the writing of the buffer
can occur from a later scheduled work queue, the oops buffer must
be protected against simultaneous dumping.

Use an atomic bit to mark when the buffer is protected. Release the
protection in between setting the buffer and the actual writing in
order for a possible panic (immediate write) to be written during
the scheduling of a previous oops (delayed write).

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 drivers/mtd/mtdoops.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 774970bfcf85..8bbfba40a554 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -52,6 +52,7 @@ static struct mtdoops_context {
 	int nextcount;
 	unsigned long *oops_page_used;
 
+	unsigned long oops_buf_busy;
 	void *oops_buf;
 } oops_cxt;
 
@@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	u32 *hdr;
 	int ret;
 
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
+
 	/* Add mtdoops header to the buffer */
 	hdr = cxt->oops_buf;
 	hdr[0] = cxt->nextcount;
@@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 				      record_size, &retlen, cxt->oops_buf);
 		if (ret == -EOPNOTSUPP) {
 			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
-			return;
+			goto out;
 		}
 	} else
 		ret = mtd_write(mtd, cxt->nextpage * record_size,
@@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	memset(cxt->oops_buf, 0xff, record_size);
 
 	mtdoops_inc_counter(cxt);
+out:
+	clear_bit(0, &cxt->oops_buf_busy);
 }
 
 static void mtdoops_workfunc_write(struct work_struct *work)
@@ -276,8 +282,11 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
 	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
+	clear_bit(0, &cxt->oops_buf_busy);
 
 	if (reason != KMSG_DUMP_OOPS) {
 		/* Panics must be written immediately */
@@ -394,6 +403,7 @@ static int __init mtdoops_init(void)
 		return -ENOMEM;
 	}
 	memset(cxt->oops_buf, 0xff, record_size);
+	cxt->oops_buf_busy = 0;
 
 	INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase);
 	INIT_WORK(&cxt->work_write, mtdoops_workfunc_write);
-- 
2.20.1

[PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[John Ogness]

The kmsg_dumper can be called from any context and CPU, possibly
from multiple CPUs simultaneously. Since the writing of the buffer
can occur from a later scheduled work queue, the oops buffer must
be protected against simultaneous dumping.

Use an atomic bit to mark when the buffer is protected. Release the
protection in between setting the buffer and the actual writing in
order for a possible panic (immediate write) to be written during
the scheduling of a previous oops (delayed write).

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 drivers/mtd/mtdoops.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 774970bfcf85..8bbfba40a554 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -52,6 +52,7 @@ static struct mtdoops_context {
 	int nextcount;
 	unsigned long *oops_page_used;
 
+	unsigned long oops_buf_busy;
 	void *oops_buf;
 } oops_cxt;
 
@@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	u32 *hdr;
 	int ret;
 
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
+
 	/* Add mtdoops header to the buffer */
 	hdr = cxt->oops_buf;
 	hdr[0] = cxt->nextcount;
@@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 				      record_size, &retlen, cxt->oops_buf);
 		if (ret == -EOPNOTSUPP) {
 			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
-			return;
+			goto out;
 		}
 	} else
 		ret = mtd_write(mtd, cxt->nextpage * record_size,
@@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	memset(cxt->oops_buf, 0xff, record_size);
 
 	mtdoops_inc_counter(cxt);
+out:
+	clear_bit(0, &cxt->oops_buf_busy);
 }
 
 static void mtdoops_workfunc_write(struct work_struct *work)
@@ -276,8 +282,11 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
 	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
+	clear_bit(0, &cxt->oops_buf_busy);
 
 	if (reason != KMSG_DUMP_OOPS) {
 		/* Panics must be written immediately */
@@ -394,6 +403,7 @@ static int __init mtdoops_init(void)
 		return -ENOMEM;
 	}
 	memset(cxt->oops_buf, 0xff, record_size);
+	cxt->oops_buf_busy = 0;
 
 	INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase);
 	INIT_WORK(&cxt->work_write, mtdoops_workfunc_write);
-- 
2.20.1


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

[PATCH next v3 03/15] printk: limit second loop of syslog_print_all

[John Ogness]

The second loop of syslog_print_all() subtracts lengths that were
added in the first loop. With commit b031a684bfd0 ("printk: remove
logbuf_lock writer-protection of ringbuffer") it is possible that
records are (over)written during syslog_print_all(). This allows the
possibility of the second loop subtracting lengths that were never
added in the first loop.

This situation can result in syslog_print_all() filling the buffer
starting from a later record, even though there may have been room
to fit the earlier record(s) as well.

Fixes: b031a684bfd0 ("printk: remove logbuf_lock writer-protection of ringbuffer")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 575a34b88936..77ae2704e979 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1494,6 +1494,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
+	u64 max_seq;
 	char *text;
 	int len = 0;
 	u64 seq;
@@ -1512,9 +1513,15 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
 		len += get_record_print_text_size(&info, line_count, true, time);
 
+	/*
+	 * Set an upper bound for the next loop to avoid subtracting lengths
+	 * that were never added.
+	 */
+	max_seq = seq;
+
 	/* move first record forward until length fits into the buffer */
 	prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
-		if (len <= size)
+		if (len <= size || info.seq >= max_seq)
 			break;
 		len -= get_record_print_text_size(&info, line_count, true, time);
 	}
-- 
2.20.1

[PATCH next v3 04/15] printk: kmsg_dump: remove unused fields

[John Ogness]

struct kmsg_dumper still contains some fields that were used to
iterate the old ringbuffer. They are no longer used. Remove them
and update the struct documentation.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kmsg_dump.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 3378bcbe585e..ae38035f1dca 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -36,6 +36,9 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
+ * @active:	Flag that specifies if this is currently dumping
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
@@ -45,8 +48,6 @@ struct kmsg_dumper {
 	bool registered;
 
 	/* private state of the kmsg iterator */
-	u32 cur_idx;
-	u32 next_idx;
 	u64 cur_seq;
 	u64 next_seq;
 };
-- 
2.20.1

[PATCH next v3 05/15] printk: refactor kmsg_dump_get_buffer()

[John Ogness]

kmsg_dump_get_buffer() requires nearly the same logic as
syslog_print_all(), but uses different variable names and
does not make use of the ringbuffer loop macros. Modify
kmsg_dump_get_buffer() so that the implementation is as similar
to syslog_print_all() as possible.

A follow-up commit will move this common logic into a
separate helper function.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 include/linux/kmsg_dump.h |  2 +-
 kernel/printk/printk.c    | 62 +++++++++++++++++++++------------------
 2 files changed, 34 insertions(+), 30 deletions(-)

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index ae38035f1dca..070c994ff19f 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -62,7 +62,7 @@ bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
 			char *line, size_t size, size_t *len);
 
 bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
-			  char *buf, size_t size, size_t *len);
+			  char *buf, size_t size, size_t *len_out);
 
 void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 77ae2704e979..ed678d84dc51 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3410,7 +3410,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
- * @len: length of line placed into buffer
+ * @len_out: length of line placed into buffer
  *
  * Start at the end of the kmsg buffer and fill the provided buffer
  * with as many of the *youngest* kmsg records that fit into it.
@@ -3424,7 +3424,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * read.
  */
 bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
-			  char *buf, size_t size, size_t *len)
+			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
 	unsigned int line_count;
@@ -3432,12 +3432,10 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	unsigned long flags;
 	u64 seq;
 	u64 next_seq;
-	size_t l = 0;
+	size_t len = 0;
 	bool ret = false;
 	bool time = printk_time;
 
-	prb_rec_init_rd(&r, &info, buf, size);
-
 	if (!dumper->active || !buf || !size)
 		goto out;
 
@@ -3455,48 +3453,54 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 	}
 
-	/* calculate length of entire buffer */
-	seq = dumper->cur_seq;
-	while (prb_read_valid_info(prb, seq, &info, &line_count)) {
-		if (r.info->seq >= dumper->next_seq)
+	/*
+	 * Find first record that fits, including all following records,
+	 * into the user-provided buffer for this dump.
+	 */
+
+	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
+		if (info.seq >= dumper->next_seq)
 			break;
-		l += get_record_print_text_size(&info, line_count, syslog, time);
-		seq = r.info->seq + 1;
+		len += get_record_print_text_size(&info, line_count, syslog, time);
 	}
 
-	/* move first record forward until length fits into the buffer */
-	seq = dumper->cur_seq;
-	while (l >= size && prb_read_valid_info(prb, seq,
-						&info, &line_count)) {
-		if (r.info->seq >= dumper->next_seq)
+	/*
+	 * Move first record forward until length fits into the buffer. Ignore
+	 * newest messages that were not counted in the above cycle. Messages
+	 * might appear and get lost in the meantime. This is the best effort
+	 * that prevents an infinite loop.
+	 */
+	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
+		if (len < size || info.seq >= dumper->next_seq)
 			break;
-		l -= get_record_print_text_size(&info, line_count, syslog, time);
-		seq = r.info->seq + 1;
+		len -= get_record_print_text_size(&info, line_count, syslog, time);
 	}
 
-	/* last message in next interation */
+	/*
+	 * Next kmsg_dump_get_buffer() invocation will dump block of
+	 * older records stored right before this one.
+	 */
 	next_seq = seq;
 
-	/* actually read text into the buffer now */
-	l = 0;
-	while (prb_read_valid(prb, seq, &r)) {
+	prb_rec_init_rd(&r, &info, buf, size);
+
+	len = 0;
+	prb_for_each_record(seq, prb, seq, &r) {
 		if (r.info->seq >= dumper->next_seq)
 			break;
 
-		l += record_print_text(&r, syslog, time);
+		len += record_print_text(&r, syslog, time);
 
-		/* adjust record to store to remaining buffer space */
-		prb_rec_init_rd(&r, &info, buf + l, size - l);
-
-		seq = r.info->seq + 1;
+		/* Adjust record to store to remaining buffer space. */
+		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
 	dumper->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
-	if (len)
-		*len = l;
+	if (len_out)
+		*len_out = len;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
-- 
2.20.1

[PATCH next v3 06/15] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code

[John Ogness]

The logic for finding records to fit into a buffer is the same for
kmsg_dump_get_buffer() and syslog_print_all(). Introduce a helper
function find_first_fitting_seq() to handle this logic.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 87 ++++++++++++++++++++++++------------------
 1 file changed, 50 insertions(+), 37 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ed678d84dc51..9a5f9ccc46ea 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1421,6 +1421,50 @@ static size_t get_record_print_text_size(struct printk_info *info,
 	return ((prefix_len * line_count) + info->text_len + 1);
 }
 
+/*
+ * Beginning with @start_seq, find the first record where it and all following
+ * records up to (but not including) @max_seq fit into @size.
+ *
+ * @max_seq is simply an upper bound and does not need to exist. If the caller
+ * does not require an upper bound, -1 can be used for @max_seq.
+ */
+static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
+				  bool syslog, bool time)
+{
+	struct printk_info info;
+	unsigned int line_count;
+	size_t len = 0;
+	u64 seq;
+
+	/* Determine the size of the records up to @max_seq. */
+	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+		if (info.seq >= max_seq)
+			break;
+		len += get_record_print_text_size(&info, line_count, syslog, time);
+	}
+
+	/*
+	 * Adjust the upper bound for the next loop to avoid subtracting
+	 * lengths that were never added.
+	 */
+	if (seq < max_seq)
+		max_seq = seq;
+
+	/*
+	 * Move first record forward until length fits into the buffer. Ignore
+	 * newest messages that were not counted in the above cycle. Messages
+	 * might appear and get lost in the meantime. This is a best effort
+	 * that prevents an infinite loop that could occur with a retry.
+	 */
+	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
+		if (len <= size || info.seq >= max_seq)
+			break;
+		len -= get_record_print_text_size(&info, line_count, syslog, time);
+	}
+
+	return seq;
+}
+
 static int syslog_print(char __user *buf, int size)
 {
 	struct printk_info info;
@@ -1492,9 +1536,7 @@ static int syslog_print(char __user *buf, int size)
 static int syslog_print_all(char __user *buf, int size, bool clear)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
-	u64 max_seq;
 	char *text;
 	int len = 0;
 	u64 seq;
@@ -1510,21 +1552,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
 	 */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
-		len += get_record_print_text_size(&info, line_count, true, time);
-
-	/*
-	 * Set an upper bound for the next loop to avoid subtracting lengths
-	 * that were never added.
-	 */
-	max_seq = seq;
-
-	/* move first record forward until length fits into the buffer */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
-		if (len <= size || info.seq >= max_seq)
-			break;
-		len -= get_record_print_text_size(&info, line_count, true, time);
-	}
+	seq = find_first_fitting_seq(clear_seq, -1, size, true, time);
 
 	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
 
@@ -3427,7 +3455,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
 	unsigned long flags;
 	u64 seq;
@@ -3455,26 +3482,12 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	/*
 	 * Find first record that fits, including all following records,
-	 * into the user-provided buffer for this dump.
+	 * into the user-provided buffer for this dump. Pass in size-1
+	 * because this function (by way of record_print_text()) will
+	 * not write more than size-1 bytes of text into @buf.
 	 */
-
-	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
-		if (info.seq >= dumper->next_seq)
-			break;
-		len += get_record_print_text_size(&info, line_count, syslog, time);
-	}
-
-	/*
-	 * Move first record forward until length fits into the buffer. Ignore
-	 * newest messages that were not counted in the above cycle. Messages
-	 * might appear and get lost in the meantime. This is the best effort
-	 * that prevents an infinite loop.
-	 */
-	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
-		if (len < size || info.seq >= dumper->next_seq)
-			break;
-		len -= get_record_print_text_size(&info, line_count, syslog, time);
-	}
+	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+				     size - 1, syslog, time);
 
 	/*
 	 * Next kmsg_dump_get_buffer() invocation will dump block of
-- 
2.20.1

[PATCH next v3 07/15] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

[John Ogness]

Instead of using "LOG_LINE_MAX + PREFIX_MAX" for temporary buffer
sizes, introduce CONSOLE_LOG_MAX. This represents the maximum size
that is allowed to be printed to the console for a single record.

Rather than setting CONSOLE_LOG_MAX to "LOG_LINE_MAX + PREFIX_MAX"
(1024), increase it to 4096. With a larger buffer size, multi-line
records that are nearly LOG_LINE_MAX in length will have a better
chance of being fully printed. (When formatting a record for the
console, each line of a multi-line record is prepended with a copy
of the prefix.)

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9a5f9ccc46ea..a60f709896dd 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -410,8 +410,13 @@ static u64 clear_seq;
 #else
 #define PREFIX_MAX		32
 #endif
+
+/* the maximum size allowed to be reserved for a record */
 #define LOG_LINE_MAX		(1024 - PREFIX_MAX)
 
+/* the maximum size of a formatted record (i.e. with prefix added per line) */
+#define CONSOLE_LOG_MAX		4096
+
 #define LOG_LEVEL(v)		((v) & 0x07)
 #define LOG_FACILITY(v)		((v) >> 3 & 0xff)
 
@@ -1472,11 +1477,11 @@ static int syslog_print(char __user *buf, int size)
 	char *text;
 	int len = 0;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	while (size > 0) {
 		size_t n;
@@ -1542,7 +1547,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	u64 seq;
 	bool time;
 
-	text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
+	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
 	if (!text)
 		return -ENOMEM;
 
@@ -1554,7 +1559,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 */
 	seq = find_first_fitting_seq(clear_seq, -1, size, true, time);
 
-	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
+	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
@@ -2187,8 +2192,7 @@ EXPORT_SYMBOL(printk);
 
 #else /* CONFIG_PRINTK */
 
-#define LOG_LINE_MAX		0
-#define PREFIX_MAX		0
+#define CONSOLE_LOG_MAX		0
 #define printk_time		false
 
 #define prb_read_valid(rb, seq, r)	false
@@ -2506,7 +2510,7 @@ static inline int can_use_console(void)
 void console_unlock(void)
 {
 	static char ext_text[CONSOLE_EXT_LOG_MAX];
-	static char text[LOG_LINE_MAX + PREFIX_MAX];
+	static char text[CONSOLE_LOG_MAX];
 	unsigned long flags;
 	bool do_cond_resched, retry;
 	struct printk_info info;
-- 
2.20.1

[PATCH next v3 08/15] printk: use seqcount_latch for clear_seq

[John Ogness]

kmsg_dump_rewind_nolock() locklessly reads @clear_seq. However,
this is not done atomically. Since @clear_seq is 64-bit, this
cannot be an atomic operation for all platforms. Therefore, use
a seqcount_latch to allow readers to always read a consistent
value.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 58 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 50 insertions(+), 8 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a60f709896dd..b78b85947312 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -402,8 +402,21 @@ static u64 console_seq;
 static u64 exclusive_console_stop_seq;
 static unsigned long console_dropped;
 
-/* the next printk record to read after the last 'clear' command */
-static u64 clear_seq;
+struct latched_seq {
+	seqcount_latch_t	latch;
+	u64			val[2];
+};
+
+/*
+ * The next printk record to read after the last 'clear' command. There are
+ * two copies (updated with seqcount_latch) so that reads can locklessly
+ * access a valid value. Writers are synchronized by @logbuf_lock.
+ */
+static struct latched_seq clear_seq = {
+	.latch		= SEQCNT_LATCH_ZERO(clear_seq.latch),
+	.val[0]		= 0,
+	.val[1]		= 0,
+};
 
 #ifdef CONFIG_PRINTK_CALLER
 #define PREFIX_MAX		48
@@ -457,6 +470,31 @@ bool printk_percpu_data_ready(void)
 	return __printk_percpu_data_ready;
 }
 
+/* Must be called under logbuf_lock. */
+static void latched_seq_write(struct latched_seq *ls, u64 val)
+{
+	raw_write_seqcount_latch(&ls->latch);
+	ls->val[0] = val;
+	raw_write_seqcount_latch(&ls->latch);
+	ls->val[1] = val;
+}
+
+/* Can be called from any context. */
+static u64 latched_seq_read_nolock(struct latched_seq *ls)
+{
+	unsigned int seq;
+	unsigned int idx;
+	u64 val;
+
+	do {
+		seq = raw_read_seqcount_latch(&ls->latch);
+		idx = seq & 0x1;
+		val = ls->val[idx];
+	} while (read_seqcount_latch_retry(&ls->latch, seq));
+
+	return val;
+}
+
 /* Return log buffer address */
 char *log_buf_addr_get(void)
 {
@@ -801,7 +839,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
 		 * changes no global state, and does not clear anything.
 		 */
-		user->seq = clear_seq;
+		user->seq = latched_seq_read_nolock(&clear_seq);
 		break;
 	case SEEK_END:
 		/* after the last record */
@@ -960,6 +998,9 @@ void log_buf_vmcoreinfo_setup(void)
 
 	VMCOREINFO_SIZE(atomic_long_t);
 	VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
+
+	VMCOREINFO_STRUCT_SIZE(latched_seq);
+	VMCOREINFO_OFFSET(latched_seq, val);
 }
 #endif
 
@@ -1557,7 +1598,8 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
 	 */
-	seq = find_first_fitting_seq(clear_seq, -1, size, true, time);
+	seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
+				     size, true, time);
 
 	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
 
@@ -1584,7 +1626,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	}
 
 	if (clear)
-		clear_seq = seq;
+		latched_seq_write(&clear_seq, seq);
 	logbuf_unlock_irq();
 
 	kfree(text);
@@ -1594,7 +1636,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 static void syslog_clear(void)
 {
 	logbuf_lock_irq();
-	clear_seq = prb_next_seq(prb);
+	latched_seq_write(&clear_seq, prb_next_seq(prb));
 	logbuf_unlock_irq();
 }
 
@@ -3336,7 +3378,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		dumper->active = true;
 
 		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = clear_seq;
+		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
 		dumper->next_seq = prb_next_seq(prb);
 		logbuf_unlock_irqrestore(flags);
 
@@ -3534,7 +3576,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  */
 void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
 {
-	dumper->cur_seq = clear_seq;
+	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
 	dumper->next_seq = prb_next_seq(prb);
 }
 
-- 
2.20.1

[PATCH next v3 09/15] printk: use atomic64_t for devkmsg_user.seq

[John Ogness]

@user->seq is indirectly protected by @logbuf_lock. Once @logbuf_lock
is removed, @user->seq will be no longer safe from an atomicity point
of view.

In preparation for the removal of @logbuf_lock, change it to
atomic64_t to provide this safety.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index b78b85947312..82d89eec4aac 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -662,7 +662,7 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
 
 /* /dev/kmsg - userspace message inject/listen interface */
 struct devkmsg_user {
-	u64 seq;
+	atomic64_t seq;
 	struct ratelimit_state rs;
 	struct mutex lock;
 	char buf[CONSOLE_EXT_LOG_MAX];
@@ -763,7 +763,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		return ret;
 
 	logbuf_lock_irq();
-	if (!prb_read_valid(prb, user->seq, r)) {
+	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
 		if (file->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
 			logbuf_unlock_irq();
@@ -772,15 +772,15 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 
 		logbuf_unlock_irq();
 		ret = wait_event_interruptible(log_wait,
-					prb_read_valid(prb, user->seq, r));
+				prb_read_valid(prb, atomic64_read(&user->seq), r));
 		if (ret)
 			goto out;
 		logbuf_lock_irq();
 	}
 
-	if (r->info->seq != user->seq) {
+	if (r->info->seq != atomic64_read(&user->seq)) {
 		/* our last seen message is gone, return error and reset */
-		user->seq = r->info->seq;
+		atomic64_set(&user->seq, r->info->seq);
 		ret = -EPIPE;
 		logbuf_unlock_irq();
 		goto out;
@@ -791,7 +791,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 				  &r->text_buf[0], r->info->text_len,
 				  &r->info->dev_info);
 
-	user->seq = r->info->seq + 1;
+	atomic64_set(&user->seq, r->info->seq + 1);
 	logbuf_unlock_irq();
 
 	if (len > count) {
@@ -831,7 +831,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	switch (whence) {
 	case SEEK_SET:
 		/* the first record */
-		user->seq = prb_first_valid_seq(prb);
+		atomic64_set(&user->seq, prb_first_valid_seq(prb));
 		break;
 	case SEEK_DATA:
 		/*
@@ -839,11 +839,11 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
 		 * changes no global state, and does not clear anything.
 		 */
-		user->seq = latched_seq_read_nolock(&clear_seq);
+		atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
 		break;
 	case SEEK_END:
 		/* after the last record */
-		user->seq = prb_next_seq(prb);
+		atomic64_set(&user->seq, prb_next_seq(prb));
 		break;
 	default:
 		ret = -EINVAL;
@@ -864,9 +864,9 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 	poll_wait(file, &log_wait, wait);
 
 	logbuf_lock_irq();
-	if (prb_read_valid_info(prb, user->seq, &info, NULL)) {
+	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
 		/* return error when data has vanished underneath us */
-		if (info.seq != user->seq)
+		if (info.seq != atomic64_read(&user->seq))
 			ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
 		else
 			ret = EPOLLIN|EPOLLRDNORM;
@@ -905,7 +905,7 @@ static int devkmsg_open(struct inode *inode, struct file *file)
 			&user->text_buf[0], sizeof(user->text_buf));
 
 	logbuf_lock_irq();
-	user->seq = prb_first_valid_seq(prb);
+	atomic64_set(&user->seq, prb_first_valid_seq(prb));
 	logbuf_unlock_irq();
 
 	file->private_data = user;
-- 
2.20.1

[PATCH next v3 10/15] printk: add syslog_lock

[John Ogness]

The global variables @syslog_seq, @syslog_partial, @syslog_time
and write access to @clear_seq are protected by @logbuf_lock.
Once @logbuf_lock is removed, these variables will need their
own synchronization method. Introduce @syslog_lock for this
purpose.

@syslog_lock is a raw_spin_lock for now. This simplifies the
transition to removing @logbuf_lock. Once @logbuf_lock and the
safe buffers are removed, @syslog_lock can change to spin_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 kernel/printk/printk.c | 41 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82d89eec4aac..c2ed7db8930b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -390,8 +390,12 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
 		printk_safe_exit_irqrestore(flags);	\
 	} while (0)
 
+/* syslog_lock protects syslog_* variables and write access to clear_seq. */
+static DEFINE_RAW_SPINLOCK(syslog_lock);
+
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
+/* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
 static u64 syslog_seq;
 static size_t syslog_partial;
@@ -410,7 +414,7 @@ struct latched_seq {
 /*
  * The next printk record to read after the last 'clear' command. There are
  * two copies (updated with seqcount_latch) so that reads can locklessly
- * access a valid value. Writers are synchronized by @logbuf_lock.
+ * access a valid value. Writers are synchronized by @syslog_lock.
  */
 static struct latched_seq clear_seq = {
 	.latch		= SEQCNT_LATCH_ZERO(clear_seq.latch),
@@ -470,7 +474,7 @@ bool printk_percpu_data_ready(void)
 	return __printk_percpu_data_ready;
 }
 
-/* Must be called under logbuf_lock. */
+/* Must be called under syslog_lock. */
 static void latched_seq_write(struct latched_seq *ls, u64 val)
 {
 	raw_write_seqcount_latch(&ls->latch);
@@ -1529,7 +1533,9 @@ static int syslog_print(char __user *buf, int size)
 		size_t skip;
 
 		logbuf_lock_irq();
+		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid(prb, syslog_seq, &r)) {
+			raw_spin_unlock(&syslog_lock);
 			logbuf_unlock_irq();
 			break;
 		}
@@ -1559,6 +1565,7 @@ static int syslog_print(char __user *buf, int size)
 			syslog_partial += n;
 		} else
 			n = 0;
+		raw_spin_unlock(&syslog_lock);
 		logbuf_unlock_irq();
 
 		if (!n)
@@ -1625,8 +1632,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 			break;
 	}
 
-	if (clear)
+	if (clear) {
+		raw_spin_lock(&syslog_lock);
 		latched_seq_write(&clear_seq, seq);
+		raw_spin_unlock(&syslog_lock);
+	}
 	logbuf_unlock_irq();
 
 	kfree(text);
@@ -1636,10 +1646,24 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 static void syslog_clear(void)
 {
 	logbuf_lock_irq();
+	raw_spin_lock(&syslog_lock);
 	latched_seq_write(&clear_seq, prb_next_seq(prb));
+	raw_spin_unlock(&syslog_lock);
 	logbuf_unlock_irq();
 }
 
+/* Return a consistent copy of @syslog_seq. */
+static u64 read_syslog_seq_irq(void)
+{
+	u64 seq;
+
+	raw_spin_lock_irq(&syslog_lock);
+	seq = syslog_seq;
+	raw_spin_unlock_irq(&syslog_lock);
+
+	return seq;
+}
+
 int do_syslog(int type, char __user *buf, int len, int source)
 {
 	struct printk_info info;
@@ -1663,8 +1687,9 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			return 0;
 		if (!access_ok(buf, len))
 			return -EFAULT;
+
 		error = wait_event_interruptible(log_wait,
-				prb_read_valid(prb, syslog_seq, NULL));
+				prb_read_valid(prb, read_syslog_seq_irq(), NULL));
 		if (error)
 			return error;
 		error = syslog_print(buf, len);
@@ -1713,8 +1738,10 @@ int do_syslog(int type, char __user *buf, int len, int source)
 	/* Number of chars in the log buffer */
 	case SYSLOG_ACTION_SIZE_UNREAD:
 		logbuf_lock_irq();
+		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
 			/* No unread messages. */
+			raw_spin_unlock(&syslog_lock);
 			logbuf_unlock_irq();
 			return 0;
 		}
@@ -1743,6 +1770,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			}
 			error -= syslog_partial;
 		}
+		raw_spin_unlock(&syslog_lock);
 		logbuf_unlock_irq();
 		break;
 	/* Size of the log buffer */
@@ -2992,7 +3020,12 @@ void register_console(struct console *newcon)
 		 */
 		exclusive_console = newcon;
 		exclusive_console_stop_seq = console_seq;
+
+		/* Get a consistent copy of @syslog_seq. */
+		raw_spin_lock(&syslog_lock);
 		console_seq = syslog_seq;
+		raw_spin_unlock(&syslog_lock);
+
 		logbuf_unlock_irqrestore(flags);
 	}
 	console_unlock();
-- 
2.20.1

[PATCH next v3 11/15] printk: kmsg_dumper: remove @active field

[John Ogness]

All 6 kmsg_dumpers do not benefit from the @active flag:

  (provide their own synchronization)
  - arch/powerpc/kernel/nvram_64.c
  - arch/um/kernel/kmsg_dump.c
  - drivers/mtd/mtdoops.c
  - fs/pstore/platform.c

  (only dump on KMSG_DUMP_PANIC, which does not require
  synchronization)
  - arch/powerpc/platforms/powernv/opal-kmsg.c
  - drivers/hv/vmbus_drv.c

The other 2 kmsg_dump users also do not rely on @active:

  (hard-code @active to always be true)
  - arch/powerpc/xmon/xmon.c
  - kernel/debug/kdb/kdb_main.c

Therefore, @active can be removed.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/xmon/xmon.c    |  2 +-
 include/linux/kmsg_dump.h   |  2 --
 kernel/debug/kdb/kdb_main.c |  2 +-
 kernel/printk/printk.c      | 10 +---------
 4 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 3fe37495f63d..80ed3e1becf9 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	unsigned char buf[128];
 	size_t len;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 070c994ff19f..84eaa2090efa 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -36,7 +36,6 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @active:	Flag that specifies if this is currently dumping
  * @cur_seq:	Points to the oldest message to dump
  * @next_seq:	Points after the newest message to dump
  */
@@ -44,7 +43,6 @@ struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
-	bool active;
 	bool registered;
 
 	/* private state of the kmsg iterator */
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 930ac1b25ec7..315169d5e119 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	size_t len;
 	char buf[201];
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c2ed7db8930b..45cb3e9c62c5 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3408,8 +3408,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-		dumper->active = true;
-
 		logbuf_lock_irqsave(flags);
 		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
 		dumper->next_seq = prb_next_seq(prb);
@@ -3417,9 +3415,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 
 		/* invoke dumper which will iterate over records */
 		dumper->dump(dumper, reason);
-
-		/* reset iterator */
-		dumper->active = false;
 	}
 	rcu_read_unlock();
 }
@@ -3454,9 +3449,6 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	prb_rec_init_rd(&r, &info, line, size);
 
-	if (!dumper->active)
-		goto out;
-
 	/* Read text or count text lines? */
 	if (line) {
 		if (!prb_read_valid(prb, dumper->cur_seq, &r))
@@ -3542,7 +3534,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	bool ret = false;
 	bool time = printk_time;
 
-	if (!dumper->active || !buf || !size)
+	if (!buf || !size)
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-- 
2.20.1

[PATCH next v3 11/15] printk: kmsg_dumper: remove @active field

[John Ogness]

All 6 kmsg_dumpers do not benefit from the @active flag:

  (provide their own synchronization)
  - arch/powerpc/kernel/nvram_64.c
  - arch/um/kernel/kmsg_dump.c
  - drivers/mtd/mtdoops.c
  - fs/pstore/platform.c

  (only dump on KMSG_DUMP_PANIC, which does not require
  synchronization)
  - arch/powerpc/platforms/powernv/opal-kmsg.c
  - drivers/hv/vmbus_drv.c

The other 2 kmsg_dump users also do not rely on @active:

  (hard-code @active to always be true)
  - arch/powerpc/xmon/xmon.c
  - kernel/debug/kdb/kdb_main.c

Therefore, @active can be removed.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/xmon/xmon.c    |  2 +-
 include/linux/kmsg_dump.h   |  2 --
 kernel/debug/kdb/kdb_main.c |  2 +-
 kernel/printk/printk.c      | 10 +---------
 4 files changed, 3 insertions(+), 13 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 3fe37495f63d..80ed3e1becf9 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	unsigned char buf[128];
 	size_t len;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 070c994ff19f..84eaa2090efa 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -36,7 +36,6 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @active:	Flag that specifies if this is currently dumping
  * @cur_seq:	Points to the oldest message to dump
  * @next_seq:	Points after the newest message to dump
  */
@@ -44,7 +43,6 @@ struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
-	bool active;
 	bool registered;
 
 	/* private state of the kmsg iterator */
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 930ac1b25ec7..315169d5e119 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dumper dumper;
 	size_t len;
 	char buf[201];
 
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c2ed7db8930b..45cb3e9c62c5 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3408,8 +3408,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-		dumper->active = true;
-
 		logbuf_lock_irqsave(flags);
 		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
 		dumper->next_seq = prb_next_seq(prb);
@@ -3417,9 +3415,6 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 
 		/* invoke dumper which will iterate over records */
 		dumper->dump(dumper, reason);
-
-		/* reset iterator */
-		dumper->active = false;
 	}
 	rcu_read_unlock();
 }
@@ -3454,9 +3449,6 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	prb_rec_init_rd(&r, &info, line, size);
 
-	if (!dumper->active)
-		goto out;
-
 	/* Read text or count text lines? */
 	if (line) {
 		if (!prb_read_valid(prb, dumper->cur_seq, &r))
@@ -3542,7 +3534,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	bool ret = false;
 	bool time = printk_time;
 
-	if (!dumper->active || !buf || !size)
+	if (!buf || !size)
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-- 
2.20.1

[PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

This change also means that the kmsg_dumper dump() callback no
longer needs to pass in the kmsg_dumper as an argument. If
kmsg_dumpers want to access the kernel logs, they can use the new
iterator.

Update the kmsg_dumper callback prototype. Update code that accesses
the kernel logs using the kmsg_dumper structure to use the new
kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
call to kmsg_dump_rewind() to initialize the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/kernel/nvram_64.c             | 14 +++---
 arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
 arch/powerpc/xmon/xmon.c                   |  6 +--
 arch/um/kernel/kmsg_dump.c                 |  8 +--
 drivers/hv/vmbus_drv.c                     |  7 +--
 drivers/mtd/mtdoops.c                      |  8 +--
 fs/pstore/platform.c                       |  8 +--
 include/linux/kmsg_dump.h                  | 38 ++++++++-------
 kernel/debug/kdb/kdb_main.c                | 10 ++--
 kernel/printk/printk.c                     | 57 ++++++++++------------
 10 files changed, 81 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..5a64b24a91c2 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
 	NULL
 };
 
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+static void oops_to_nvram(enum kmsg_dump_reason reason);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * that we think will compress sufficiently to fit in the lnx,oops-log
  * partition.  If that's too much, go back and capture uncompressed text.
  */
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+static void oops_to_nvram(enum kmsg_dump_reason reason)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da98..a7bd6ac681f4 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -19,8 +19,7 @@
  * may not be completely printed.  This function does not actually dump the
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
-static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 80ed3e1becf9..5978b90a885f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 4869e2cc787c..9fbc5e5b1023 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -7,9 +7,9 @@
 #include <shared/kern.h>
 #include <os.h>
 
-static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
@@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (!spin_trylock(&lock))
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 10dce9f91216..1b858f280e22 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
  * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
  * buffer and call into Hyper-V to transfer the data.
  */
-static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+static void hv_kmsg_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 	phys_addr_t panic_pa;
 
@@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 8bbfba40a554..d179b726a1c9 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
 	mtdoops_inc_counter(cxt);
 }
 
-static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+static void mtdoops_do_dump(enum kmsg_dump_reason reason)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	if (test_and_set_bit(0, &cxt->oops_buf_busy))
 		return;
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 	clear_bit(0, &cxt->oops_buf_busy);
 
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d963ae7902f9..edfc9504e024 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
  * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
  * end of the buffer.
  */
-static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+static void pstore_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..5d3bf20f9f0a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -36,35 +46,29 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 315169d5e119..8544d7a55a57 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	size_t len;
 	char buf[201];
 
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 45cb3e9c62c5..e58ccc368348 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
 	struct kmsg_dumper *dumper;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		if (reason > max_reason)
 			continue;
 
-		/* initialize iterator with data about the stored records */
-		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-		dumper->next_seq = prb_next_seq(prb);
-		logbuf_unlock_irqrestore(flags);
-
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
+		dumper->dump(reason);
 	}
 	rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
@@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
@@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
@@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	 * because this function (by way of record_print_text()) will
 	 * not write more than size-1 bytes of text into @buf.
 	 */
-	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
 				     size - 1, syslog, time);
 
 	/*
@@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
-		if (r.info->seq >= dumper->next_seq)
+		if (r.info->seq >= iter->next_seq)
 			break;
 
 		len += record_print_text(&r, syslog, time);
@@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
@@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
-	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

[PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

This change also means that the kmsg_dumper dump() callback no
longer needs to pass in the kmsg_dumper as an argument. If
kmsg_dumpers want to access the kernel logs, they can use the new
iterator.

Update the kmsg_dumper callback prototype. Update code that accesses
the kernel logs using the kmsg_dumper structure to use the new
kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
call to kmsg_dump_rewind() to initialize the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/kernel/nvram_64.c             | 14 +++---
 arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
 arch/powerpc/xmon/xmon.c                   |  6 +--
 arch/um/kernel/kmsg_dump.c                 |  8 +--
 drivers/hv/vmbus_drv.c                     |  7 +--
 drivers/mtd/mtdoops.c                      |  8 +--
 fs/pstore/platform.c                       |  8 +--
 include/linux/kmsg_dump.h                  | 38 ++++++++-------
 kernel/debug/kdb/kdb_main.c                | 10 ++--
 kernel/printk/printk.c                     | 57 ++++++++++------------
 10 files changed, 81 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..5a64b24a91c2 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
 	NULL
 };
 
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+static void oops_to_nvram(enum kmsg_dump_reason reason);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * that we think will compress sufficiently to fit in the lnx,oops-log
  * partition.  If that's too much, go back and capture uncompressed text.
  */
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+static void oops_to_nvram(enum kmsg_dump_reason reason)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da98..a7bd6ac681f4 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -19,8 +19,7 @@
  * may not be completely printed.  This function does not actually dump the
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
-static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 80ed3e1becf9..5978b90a885f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 4869e2cc787c..9fbc5e5b1023 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -7,9 +7,9 @@
 #include <shared/kern.h>
 #include <os.h>
 
-static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
@@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (!spin_trylock(&lock))
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 10dce9f91216..1b858f280e22 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
  * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
  * buffer and call into Hyper-V to transfer the data.
  */
-static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+static void hv_kmsg_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 	phys_addr_t panic_pa;
 
@@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 8bbfba40a554..d179b726a1c9 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
 	mtdoops_inc_counter(cxt);
 }
 
-static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+static void mtdoops_do_dump(enum kmsg_dump_reason reason)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	if (test_and_set_bit(0, &cxt->oops_buf_busy))
 		return;
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 	clear_bit(0, &cxt->oops_buf_busy);
 
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d963ae7902f9..edfc9504e024 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
  * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
  * end of the buffer.
  */
-static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+static void pstore_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..5d3bf20f9f0a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -36,35 +46,29 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 315169d5e119..8544d7a55a57 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	size_t len;
 	char buf[201];
 
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 45cb3e9c62c5..e58ccc368348 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
 	struct kmsg_dumper *dumper;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		if (reason > max_reason)
 			continue;
 
-		/* initialize iterator with data about the stored records */
-		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-		dumper->next_seq = prb_next_seq(prb);
-		logbuf_unlock_irqrestore(flags);
-
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
+		dumper->dump(reason);
 	}
 	rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
@@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
@@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
@@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	 * because this function (by way of record_print_text()) will
 	 * not write more than size-1 bytes of text into @buf.
 	 */
-	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
 				     size - 1, syslog, time);
 
 	/*
@@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
-		if (r.info->seq >= dumper->next_seq)
+		if (r.info->seq >= iter->next_seq)
 			break;
 
 		len += record_print_text(&r, syslog, time);
@@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
@@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
-	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

[PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

This change also means that the kmsg_dumper dump() callback no
longer needs to pass in the kmsg_dumper as an argument. If
kmsg_dumpers want to access the kernel logs, they can use the new
iterator.

Update the kmsg_dumper callback prototype. Update code that accesses
the kernel logs using the kmsg_dumper structure to use the new
kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
call to kmsg_dump_rewind() to initialize the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/kernel/nvram_64.c             | 14 +++---
 arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
 arch/powerpc/xmon/xmon.c                   |  6 +--
 arch/um/kernel/kmsg_dump.c                 |  8 +--
 drivers/hv/vmbus_drv.c                     |  7 +--
 drivers/mtd/mtdoops.c                      |  8 +--
 fs/pstore/platform.c                       |  8 +--
 include/linux/kmsg_dump.h                  | 38 ++++++++-------
 kernel/debug/kdb/kdb_main.c                | 10 ++--
 kernel/printk/printk.c                     | 57 ++++++++++------------
 10 files changed, 81 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..5a64b24a91c2 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
 	NULL
 };
 
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+static void oops_to_nvram(enum kmsg_dump_reason reason);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * that we think will compress sufficiently to fit in the lnx,oops-log
  * partition.  If that's too much, go back and capture uncompressed text.
  */
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+static void oops_to_nvram(enum kmsg_dump_reason reason)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da98..a7bd6ac681f4 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -19,8 +19,7 @@
  * may not be completely printed.  This function does not actually dump the
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
-static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 80ed3e1becf9..5978b90a885f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 4869e2cc787c..9fbc5e5b1023 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -7,9 +7,9 @@
 #include <shared/kern.h>
 #include <os.h>
 
-static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
@@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (!spin_trylock(&lock))
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 10dce9f91216..1b858f280e22 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
  * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
  * buffer and call into Hyper-V to transfer the data.
  */
-static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+static void hv_kmsg_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 	phys_addr_t panic_pa;
 
@@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 8bbfba40a554..d179b726a1c9 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
 	mtdoops_inc_counter(cxt);
 }
 
-static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+static void mtdoops_do_dump(enum kmsg_dump_reason reason)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	if (test_and_set_bit(0, &cxt->oops_buf_busy))
 		return;
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 	clear_bit(0, &cxt->oops_buf_busy);
 
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d963ae7902f9..edfc9504e024 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
  * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
  * end of the buffer.
  */
-static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+static void pstore_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..5d3bf20f9f0a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -36,35 +46,29 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 315169d5e119..8544d7a55a57 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	size_t len;
 	char buf[201];
 
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 45cb3e9c62c5..e58ccc368348 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
 	struct kmsg_dumper *dumper;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		if (reason > max_reason)
 			continue;
 
-		/* initialize iterator with data about the stored records */
-		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-		dumper->next_seq = prb_next_seq(prb);
-		logbuf_unlock_irqrestore(flags);
-
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
+		dumper->dump(reason);
 	}
 	rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
@@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
@@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
@@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	 * because this function (by way of record_print_text()) will
 	 * not write more than size-1 bytes of text into @buf.
 	 */
-	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
 				     size - 1, syslog, time);
 
 	/*
@@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
-		if (r.info->seq >= dumper->next_seq)
+		if (r.info->seq >= iter->next_seq)
 			break;
 
 		len += record_print_text(&r, syslog, time);
@@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
@@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
-	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

[PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

This change also means that the kmsg_dumper dump() callback no
longer needs to pass in the kmsg_dumper as an argument. If
kmsg_dumpers want to access the kernel logs, they can use the new
iterator.

Update the kmsg_dumper callback prototype. Update code that accesses
the kernel logs using the kmsg_dumper structure to use the new
kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
call to kmsg_dump_rewind() to initialize the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 arch/powerpc/kernel/nvram_64.c             | 14 +++---
 arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
 arch/powerpc/xmon/xmon.c                   |  6 +--
 arch/um/kernel/kmsg_dump.c                 |  8 +--
 drivers/hv/vmbus_drv.c                     |  7 +--
 drivers/mtd/mtdoops.c                      |  8 +--
 fs/pstore/platform.c                       |  8 +--
 include/linux/kmsg_dump.h                  | 38 ++++++++-------
 kernel/debug/kdb/kdb_main.c                | 10 ++--
 kernel/printk/printk.c                     | 57 ++++++++++------------
 10 files changed, 81 insertions(+), 78 deletions(-)

diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
index 532f22637783..5a64b24a91c2 100644
--- a/arch/powerpc/kernel/nvram_64.c
+++ b/arch/powerpc/kernel/nvram_64.c
@@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
 	NULL
 };
 
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+static void oops_to_nvram(enum kmsg_dump_reason reason);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * that we think will compress sufficiently to fit in the lnx,oops-log
  * partition.  If that's too much, go back and capture uncompressed text.
  */
-static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+static void oops_to_nvram(enum kmsg_dump_reason reason)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
index 6c3bc4b4da98..a7bd6ac681f4 100644
--- a/arch/powerpc/platforms/powernv/opal-kmsg.c
+++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
@@ -19,8 +19,7 @@
  * may not be completely printed.  This function does not actually dump the
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
-static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 80ed3e1becf9..5978b90a885f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind_nolock(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index 4869e2cc787c..9fbc5e5b1023 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -7,9 +7,9 @@
 #include <shared/kern.h>
 #include <os.h>
 
-static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
@@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (!spin_trylock(&lock))
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 10dce9f91216..1b858f280e22 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
  * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
  * buffer and call into Hyper-V to transfer the data.
  */
-static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+static void hv_kmsg_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 	phys_addr_t panic_pa;
 
@@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (bytes_written)
 		hyperv_report_panic_msg(panic_pa, bytes_written);
diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
index 8bbfba40a554..d179b726a1c9 100644
--- a/drivers/mtd/mtdoops.c
+++ b/drivers/mtd/mtdoops.c
@@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
 	mtdoops_inc_counter(cxt);
 }
 
-static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+static void mtdoops_do_dump(enum kmsg_dump_reason reason)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
+	kmsg_dump_rewind(&iter);
+
 	if (test_and_set_bit(0, &cxt->oops_buf_busy))
 		return;
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
 	clear_bit(0, &cxt->oops_buf_busy);
 
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d963ae7902f9..edfc9504e024 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
  * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
  * end of the buffer.
  */
-static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+static void pstore_dump(enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..5d3bf20f9f0a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -36,35 +46,29 @@ enum kmsg_dump_reason {
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 315169d5e119..8544d7a55a57 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
 	int adjust = 0;
 	int n = 0;
 	int skip = 0;
-	struct kmsg_dumper dumper;
+	struct kmsg_dump_iter iter;
 	size_t len;
 	char buf[201];
 
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&dumper);
-	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind_nolock(&iter);
+	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 45cb3e9c62c5..e58ccc368348 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
 	struct kmsg_dumper *dumper;
-	unsigned long flags;
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 		if (reason > max_reason)
 			continue;
 
-		/* initialize iterator with data about the stored records */
-		logbuf_lock_irqsave(flags);
-		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-		dumper->next_seq = prb_next_seq(prb);
-		logbuf_unlock_irqrestore(flags);
-
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
+		dumper->dump(reason);
 	}
 	rcu_read_unlock();
 }
 
 /**
  * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
@@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	/* Read text or count text lines? */
 	if (line) {
-		if (!prb_read_valid(prb, dumper->cur_seq, &r))
+		if (!prb_read_valid(prb, iter->cur_seq, &r))
 			goto out;
 		l = record_print_text(&r, syslog, printk_time);
 	} else {
-		if (!prb_read_valid_info(prb, dumper->cur_seq,
+		if (!prb_read_valid_info(prb, iter->cur_seq,
 					 &info, &line_count)) {
 			goto out;
 		}
@@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 	}
 
-	dumper->cur_seq = r.info->seq + 1;
+	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
 	if (len)
@@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
 
 /**
  * kmsg_dump_get_line - retrieve one kmsg log line
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len)
 {
 	unsigned long flags;
 	bool ret;
 
 	logbuf_lock_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
+	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
 	logbuf_unlock_irqrestore(flags);
 
 	return ret;
@@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
  * kmsg_dump_get_buffer - copy kmsg log lines
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @buf: buffer to copy the line to
  * @size: maximum size of the buffer
@@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
  * A return value of FALSE indicates that there are no more records to
  * read.
  */
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
@@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		goto out;
 
 	logbuf_lock_irqsave(flags);
-	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
-		if (info.seq != dumper->cur_seq) {
+	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
+		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
-			dumper->cur_seq = info.seq;
+			iter->cur_seq = info.seq;
 		}
 	}
 
 	/* last entry */
-	if (dumper->cur_seq >= dumper->next_seq) {
+	if (iter->cur_seq >= iter->next_seq) {
 		logbuf_unlock_irqrestore(flags);
 		goto out;
 	}
@@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 	 * because this function (by way of record_print_text()) will
 	 * not write more than size-1 bytes of text into @buf.
 	 */
-	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
 				     size - 1, syslog, time);
 
 	/*
@@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	len = 0;
 	prb_for_each_record(seq, prb, seq, &r) {
-		if (r.info->seq >= dumper->next_seq)
+		if (r.info->seq >= iter->next_seq)
 			break;
 
 		len += record_print_text(&r, syslog, time);
@@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 		prb_rec_init_rd(&r, &info, buf + len, size - len);
 	}
 
-	dumper->next_seq = next_seq;
+	iter->next_seq = next_seq;
 	ret = true;
 	logbuf_unlock_irqrestore(flags);
 out:
@@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
 /**
  * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
@@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
  *
  * The function is similar to kmsg_dump_rewind(), but grabs no locks.
  */
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
-	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
-	dumper->next_seq = prb_next_seq(prb);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 }
 
 /**
  * kmsg_dump_rewind - reset the iterator
- * @dumper: registered kmsg dumper
+ * @iter: kmsg dump iterator
  *
  * Reset the dumper's iterator so that kmsg_dump_get_line() and
  * kmsg_dump_get_buffer() can be called again and used multiple
  * times within the same dumper.dump() callback.
  */
-void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
 	logbuf_lock_irqsave(flags);
-	kmsg_dump_rewind_nolock(dumper);
+	kmsg_dump_rewind_nolock(iter);
 	logbuf_unlock_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1


_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um

[PATCH next v3 13/15] printk: remove logbuf_lock

[John Ogness]

Since the ringbuffer is lockless, there is no need for it to be
protected by @logbuf_lock. Remove @logbuf_lock.

@console_seq, @exclusive_console_stop_seq, @console_dropped are
protected by @console_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 kernel/printk/internal.h    |   4 +-
 kernel/printk/printk.c      | 112 ++++++++++++------------------------
 kernel/printk/printk_safe.c |  27 +++------
 3 files changed, 46 insertions(+), 97 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 3a8fd491758c..e7acc2888c8e 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -12,8 +12,6 @@
 
 #define PRINTK_NMI_CONTEXT_OFFSET	0x010000000
 
-extern raw_spinlock_t logbuf_lock;
-
 __printf(4, 0)
 int vprintk_store(int facility, int level,
 		  const struct dev_printk_info *dev_info,
@@ -59,7 +57,7 @@ void defer_console_output(void);
 __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
 
 /*
- * In !PRINTK builds we still export logbuf_lock spin_lock, console_sem
+ * In !PRINTK builds we still export console_sem
  * semaphore and some of console functions (console_unlock()/etc.), so
  * printk-safe must preserve the existing local IRQ guarantees.
  */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e58ccc368348..01385ea92e7c 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -355,41 +355,6 @@ enum log_flags {
 	LOG_CONT	= 8,	/* text is a fragment of a continuation line */
 };
 
-/*
- * The logbuf_lock protects kmsg buffer, indices, counters.  This can be taken
- * within the scheduler's rq lock. It must be released before calling
- * console_unlock() or anything else that might wake up a process.
- */
-DEFINE_RAW_SPINLOCK(logbuf_lock);
-
-/*
- * Helper macros to lock/unlock logbuf_lock and switch between
- * printk-safe/unsafe modes.
- */
-#define logbuf_lock_irq()				\
-	do {						\
-		printk_safe_enter_irq();		\
-		raw_spin_lock(&logbuf_lock);		\
-	} while (0)
-
-#define logbuf_unlock_irq()				\
-	do {						\
-		raw_spin_unlock(&logbuf_lock);		\
-		printk_safe_exit_irq();			\
-	} while (0)
-
-#define logbuf_lock_irqsave(flags)			\
-	do {						\
-		printk_safe_enter_irqsave(flags);	\
-		raw_spin_lock(&logbuf_lock);		\
-	} while (0)
-
-#define logbuf_unlock_irqrestore(flags)		\
-	do {						\
-		raw_spin_unlock(&logbuf_lock);		\
-		printk_safe_exit_irqrestore(flags);	\
-	} while (0)
-
 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
 static DEFINE_RAW_SPINLOCK(syslog_lock);
 
@@ -401,6 +366,7 @@ static u64 syslog_seq;
 static size_t syslog_partial;
 static bool syslog_time;
 
+/* All 3 protected by @console_sem. */
 /* the next printk record to write to the console */
 static u64 console_seq;
 static u64 exclusive_console_stop_seq;
@@ -766,27 +732,27 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 	if (ret)
 		return ret;
 
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
 		if (file->f_flags & O_NONBLOCK) {
 			ret = -EAGAIN;
-			logbuf_unlock_irq();
+			printk_safe_exit_irq();
 			goto out;
 		}
 
-		logbuf_unlock_irq();
+		printk_safe_exit_irq();
 		ret = wait_event_interruptible(log_wait,
 				prb_read_valid(prb, atomic64_read(&user->seq), r));
 		if (ret)
 			goto out;
-		logbuf_lock_irq();
+		printk_safe_enter_irq();
 	}
 
 	if (r->info->seq != atomic64_read(&user->seq)) {
 		/* our last seen message is gone, return error and reset */
 		atomic64_set(&user->seq, r->info->seq);
 		ret = -EPIPE;
-		logbuf_unlock_irq();
+		printk_safe_exit_irq();
 		goto out;
 	}
 
@@ -796,7 +762,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 				  &r->info->dev_info);
 
 	atomic64_set(&user->seq, r->info->seq + 1);
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 
 	if (len > count) {
 		ret = -EINVAL;
@@ -831,7 +797,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	if (offset)
 		return -ESPIPE;
 
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	switch (whence) {
 	case SEEK_SET:
 		/* the first record */
@@ -852,7 +818,7 @@ static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
 	default:
 		ret = -EINVAL;
 	}
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 	return ret;
 }
 
@@ -867,7 +833,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &log_wait, wait);
 
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
 		/* return error when data has vanished underneath us */
 		if (info.seq != atomic64_read(&user->seq))
@@ -875,7 +841,7 @@ static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
 		else
 			ret = EPOLLIN|EPOLLRDNORM;
 	}
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 
 	return ret;
 }
@@ -908,9 +874,9 @@ static int devkmsg_open(struct inode *inode, struct file *file)
 	prb_rec_init_rd(&user->record, &user->info,
 			&user->text_buf[0], sizeof(user->text_buf));
 
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	atomic64_set(&user->seq, prb_first_valid_seq(prb));
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 
 	file->private_data = user;
 	return 0;
@@ -1532,11 +1498,11 @@ static int syslog_print(char __user *buf, int size)
 		size_t n;
 		size_t skip;
 
-		logbuf_lock_irq();
+		printk_safe_enter_irq();
 		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid(prb, syslog_seq, &r)) {
 			raw_spin_unlock(&syslog_lock);
-			logbuf_unlock_irq();
+			printk_safe_exit_irq();
 			break;
 		}
 		if (r.info->seq != syslog_seq) {
@@ -1566,7 +1532,7 @@ static int syslog_print(char __user *buf, int size)
 		} else
 			n = 0;
 		raw_spin_unlock(&syslog_lock);
-		logbuf_unlock_irq();
+		printk_safe_exit_irq();
 
 		if (!n)
 			break;
@@ -1600,7 +1566,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 		return -ENOMEM;
 
 	time = printk_time;
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	/*
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
@@ -1621,12 +1587,12 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 			break;
 		}
 
-		logbuf_unlock_irq();
+		printk_safe_exit_irq();
 		if (copy_to_user(buf + len, text, textlen))
 			len = -EFAULT;
 		else
 			len += textlen;
-		logbuf_lock_irq();
+		printk_safe_enter_irq();
 
 		if (len < 0)
 			break;
@@ -1637,7 +1603,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 		latched_seq_write(&clear_seq, seq);
 		raw_spin_unlock(&syslog_lock);
 	}
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 
 	kfree(text);
 	return len;
@@ -1645,11 +1611,11 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 
 static void syslog_clear(void)
 {
-	logbuf_lock_irq();
+	printk_safe_enter_irq();
 	raw_spin_lock(&syslog_lock);
 	latched_seq_write(&clear_seq, prb_next_seq(prb));
 	raw_spin_unlock(&syslog_lock);
-	logbuf_unlock_irq();
+	printk_safe_exit_irq();
 }
 
 /* Return a consistent copy of @syslog_seq. */
@@ -1737,12 +1703,12 @@ int do_syslog(int type, char __user *buf, int len, int source)
 		break;
 	/* Number of chars in the log buffer */
 	case SYSLOG_ACTION_SIZE_UNREAD:
-		logbuf_lock_irq();
+		printk_safe_enter_irq();
 		raw_spin_lock(&syslog_lock);
 		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
 			/* No unread messages. */
 			raw_spin_unlock(&syslog_lock);
-			logbuf_unlock_irq();
+			printk_safe_exit_irq();
 			return 0;
 		}
 		if (info.seq != syslog_seq) {
@@ -1771,7 +1737,7 @@ int do_syslog(int type, char __user *buf, int len, int source)
 			error -= syslog_partial;
 		}
 		raw_spin_unlock(&syslog_lock);
-		logbuf_unlock_irq();
+		printk_safe_exit_irq();
 		break;
 	/* Size of the log buffer */
 	case SYSLOG_ACTION_SIZE_BUFFER:
@@ -2627,7 +2593,6 @@ void console_unlock(void)
 		size_t len;
 
 		printk_safe_enter_irqsave(flags);
-		raw_spin_lock(&logbuf_lock);
 skip:
 		if (!prb_read_valid(prb, console_seq, &r))
 			break;
@@ -2671,7 +2636,6 @@ void console_unlock(void)
 				console_msg_format & MSG_FORMAT_SYSLOG,
 				printk_time);
 		console_seq++;
-		raw_spin_unlock(&logbuf_lock);
 
 		/*
 		 * While actively printing out messages, if another printk()
@@ -2698,8 +2662,6 @@ void console_unlock(void)
 
 	console_locked = 0;
 
-	raw_spin_unlock(&logbuf_lock);
-
 	up_console_sem();
 
 	/*
@@ -2708,9 +2670,7 @@ void console_unlock(void)
 	 * there's a new owner and the console_unlock() from them will do the
 	 * flush, no worries.
 	 */
-	raw_spin_lock(&logbuf_lock);
 	retry = prb_read_valid(prb, console_seq, NULL);
-	raw_spin_unlock(&logbuf_lock);
 	printk_safe_exit_irqrestore(flags);
 
 	if (retry && console_trylock())
@@ -2777,9 +2737,9 @@ void console_flush_on_panic(enum con_flush_mode mode)
 	if (mode == CONSOLE_REPLAY_ALL) {
 		unsigned long flags;
 
-		logbuf_lock_irqsave(flags);
+		printk_safe_enter_irqsave(flags);
 		console_seq = prb_first_valid_seq(prb);
-		logbuf_unlock_irqrestore(flags);
+		printk_safe_exit_irqrestore(flags);
 	}
 	console_unlock();
 }
@@ -3008,7 +2968,7 @@ void register_console(struct console *newcon)
 		 * console_unlock(); will print out the buffered messages
 		 * for us.
 		 */
-		logbuf_lock_irqsave(flags);
+		printk_safe_enter_irqsave(flags);
 		/*
 		 * We're about to replay the log buffer.  Only do this to the
 		 * just-registered console to avoid excessive message spam to
@@ -3026,7 +2986,7 @@ void register_console(struct console *newcon)
 		console_seq = syslog_seq;
 		raw_spin_unlock(&syslog_lock);
 
-		logbuf_unlock_irqrestore(flags);
+		printk_safe_exit_irqrestore(flags);
 	}
 	console_unlock();
 	console_sysfs_notify();
@@ -3488,9 +3448,9 @@ bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 	unsigned long flags;
 	bool ret;
 
-	logbuf_lock_irqsave(flags);
+	printk_safe_enter_irqsave(flags);
 	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
-	logbuf_unlock_irqrestore(flags);
+	printk_safe_exit_irqrestore(flags);
 
 	return ret;
 }
@@ -3530,7 +3490,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 	if (!buf || !size)
 		goto out;
 
-	logbuf_lock_irqsave(flags);
+	printk_safe_enter_irqsave(flags);
 	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
 		if (info.seq != iter->cur_seq) {
 			/* messages are gone, move to first available one */
@@ -3540,7 +3500,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
 	/* last entry */
 	if (iter->cur_seq >= iter->next_seq) {
-		logbuf_unlock_irqrestore(flags);
+		printk_safe_exit_irqrestore(flags);
 		goto out;
 	}
 
@@ -3574,7 +3534,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 
 	iter->next_seq = next_seq;
 	ret = true;
-	logbuf_unlock_irqrestore(flags);
+	printk_safe_exit_irqrestore(flags);
 out:
 	if (len_out)
 		*len_out = len;
@@ -3610,9 +3570,9 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 	unsigned long flags;
 
-	logbuf_lock_irqsave(flags);
+	printk_safe_enter_irqsave(flags);
 	kmsg_dump_rewind_nolock(iter);
-	logbuf_unlock_irqrestore(flags);
+	printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 2e9e3ed7d63e..bbf5c1993636 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -16,7 +16,7 @@
 #include "internal.h"
 
 /*
- * printk() could not take logbuf_lock in NMI context. Instead,
+ * In NMI and safe mode, printk() avoids taking locks. Instead,
  * it uses an alternative implementation that temporary stores
  * the strings into a per-CPU buffer. The content of the buffer
  * is later flushed into the main ring buffer via IRQ work.
@@ -267,17 +267,9 @@ void printk_safe_flush(void)
 void printk_safe_flush_on_panic(void)
 {
 	/*
-	 * Make sure that we could access the main ring buffer.
+	 * Make sure that we could access the safe buffers.
 	 * Do not risk a double release when more CPUs are up.
 	 */
-	if (raw_spin_is_locked(&logbuf_lock)) {
-		if (num_online_cpus() > 1)
-			return;
-
-		debug_locks_off();
-		raw_spin_lock_init(&logbuf_lock);
-	}
-
 	if (raw_spin_is_locked(&safe_read_lock)) {
 		if (num_online_cpus() > 1)
 			return;
@@ -319,9 +311,7 @@ void noinstr printk_nmi_exit(void)
  * reordering.
  *
  * It has effect only when called in NMI context. Then printk()
- * will try to store the messages into the main logbuf directly
- * and use the per-CPU buffers only as a fallback when the lock
- * is not available.
+ * will store the messages into the main logbuf directly.
  */
 void printk_nmi_direct_enter(void)
 {
@@ -376,20 +366,21 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
 #endif
 
 	/*
-	 * Try to use the main logbuf even in NMI. But avoid calling console
+	 * Use the main logbuf even in NMI. But avoid calling console
 	 * drivers that might have their own locks.
 	 */
-	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
-	    raw_spin_trylock(&logbuf_lock)) {
+	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK)) {
+		unsigned long flags;
 		int len;
 
+		printk_safe_enter_irqsave(flags);
 		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
-		raw_spin_unlock(&logbuf_lock);
+		printk_safe_exit_irqrestore(flags);
 		defer_console_output();
 		return len;
 	}
 
-	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
+	/* Use extra buffer in NMI. */
 	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
 		return vprintk_nmi(fmt, args);
 
-- 
2.20.1

[PATCH next v3 14/15] printk: kmsg_dump: remove _nolock() variants

[John Ogness]

kmsg_dump_rewind() and kmsg_dump_get_line() are lockless, so there is
no need for _nolock() variants. Remove these functions and switch all
callers of the _nolock() variants.

The functions without _nolock() were chosen because they are already
exported to kernel modules.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/powerpc/xmon/xmon.c    |  4 +--
 include/linux/kmsg_dump.h   | 16 ----------
 kernel/debug/kdb/kdb_main.c |  8 ++---
 kernel/printk/printk.c      | 60 +++++--------------------------------
 4 files changed, 14 insertions(+), 74 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 5978b90a885f..bf7d69625a2e 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&iter);
+	kmsg_dump_rewind(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 5d3bf20f9f0a..532673b6570a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -57,17 +57,12 @@ struct kmsg_dumper {
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len);
-
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
-
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
@@ -80,13 +75,6 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
-					     bool syslog, const char *line,
-					     size_t size, size_t *len)
-{
-	return false;
-}
-
 static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
@@ -99,10 +87,6 @@ static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
-{
-}
-
 static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 8544d7a55a57..67d9f2403b52 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 01385ea92e7c..15a9bc409e0a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3373,7 +3373,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 }
 
 /**
- * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
+ * kmsg_dump_get_line - retrieve one kmsg log line
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
@@ -3388,18 +3388,18 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
- *
- * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len)
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
+			char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
+	unsigned long flags;
 	size_t l = 0;
 	bool ret = false;
 
+	printk_safe_enter_irqsave(flags);
 	prb_rec_init_rd(&r, &info, line, size);
 
 	/* Read text or count text lines? */
@@ -3420,40 +3420,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
+	printk_safe_exit_irqrestore(flags);
 	if (len)
 		*len = l;
 	return ret;
 }
-
-/**
- * kmsg_dump_get_line - retrieve one kmsg log line
- * @iter: kmsg dump iterator
- * @syslog: include the "<4>" prefixes
- * @line: buffer to copy the line to
- * @size: maximum size of the buffer
- * @len: length of line placed into buffer
- *
- * Start at the beginning of the kmsg buffer, with the oldest kmsg
- * record, and copy one record into the provided buffer.
- *
- * Consecutive calls will return the next available record moving
- * towards the end of the buffer with the youngest messages.
- *
- * A return value of FALSE indicates that there are no more records to
- * read.
- */
-bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
-			char *line, size_t size, size_t *len)
-{
-	unsigned long flags;
-	bool ret;
-
-	printk_safe_enter_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
-	printk_safe_exit_irqrestore(flags);
-
-	return ret;
-}
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
@@ -3542,22 +3513,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
-/**
- * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @iter: kmsg dump iterator
- *
- * Reset the dumper's iterator so that kmsg_dump_get_line() and
- * kmsg_dump_get_buffer() can be called again and used multiple
- * times within the same dumper.dump() callback.
- *
- * The function is similar to kmsg_dump_rewind(), but grabs no locks.
- */
-void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
-{
-	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
-	iter->next_seq = prb_next_seq(prb);
-}
-
 /**
  * kmsg_dump_rewind - reset the iterator
  * @iter: kmsg dump iterator
@@ -3571,7 +3526,8 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 	unsigned long flags;
 
 	printk_safe_enter_irqsave(flags);
-	kmsg_dump_rewind_nolock(iter);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 	printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

[PATCH next v3 14/15] printk: kmsg_dump: remove _nolock() variants

[John Ogness]

kmsg_dump_rewind() and kmsg_dump_get_line() are lockless, so there is
no need for _nolock() variants. Remove these functions and switch all
callers of the _nolock() variants.

The functions without _nolock() were chosen because they are already
exported to kernel modules.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 arch/powerpc/xmon/xmon.c    |  4 +--
 include/linux/kmsg_dump.h   | 16 ----------
 kernel/debug/kdb/kdb_main.c |  8 ++---
 kernel/printk/printk.c      | 60 +++++--------------------------------
 4 files changed, 14 insertions(+), 74 deletions(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 5978b90a885f..bf7d69625a2e 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&iter);
+	kmsg_dump_rewind(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}
diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 5d3bf20f9f0a..532673b6570a 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -57,17 +57,12 @@ struct kmsg_dumper {
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len);
-
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
-
 void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
@@ -80,13 +75,6 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
-					     bool syslog, const char *line,
-					     size_t size, size_t *len)
-{
-	return false;
-}
-
 static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
@@ -99,10 +87,6 @@ static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
-{
-}
-
 static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 8544d7a55a57..67d9f2403b52 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
 		kdb_set(2, setargs);
 	}
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, NULL, 0, NULL))
 		n++;
 
 	if (lines < 0) {
@@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
 	if (skip >= n || skip < 0)
 		return 0;
 
-	kmsg_dump_rewind_nolock(&iter);
-	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
+	kmsg_dump_rewind(&iter);
+	while (kmsg_dump_get_line(&iter, 1, buf, sizeof(buf), &len)) {
 		if (skip) {
 			skip--;
 			continue;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 01385ea92e7c..15a9bc409e0a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3373,7 +3373,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 }
 
 /**
- * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
+ * kmsg_dump_get_line - retrieve one kmsg log line
  * @iter: kmsg dump iterator
  * @syslog: include the "<4>" prefixes
  * @line: buffer to copy the line to
@@ -3388,18 +3388,18 @@ void kmsg_dump(enum kmsg_dump_reason reason)
  *
  * A return value of FALSE indicates that there are no more records to
  * read.
- *
- * The function is similar to kmsg_dump_get_line(), but grabs no locks.
  */
-bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
-			       char *line, size_t size, size_t *len)
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
+			char *line, size_t size, size_t *len)
 {
 	struct printk_info info;
 	unsigned int line_count;
 	struct printk_record r;
+	unsigned long flags;
 	size_t l = 0;
 	bool ret = false;
 
+	printk_safe_enter_irqsave(flags);
 	prb_rec_init_rd(&r, &info, line, size);
 
 	/* Read text or count text lines? */
@@ -3420,40 +3420,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 	iter->cur_seq = r.info->seq + 1;
 	ret = true;
 out:
+	printk_safe_exit_irqrestore(flags);
 	if (len)
 		*len = l;
 	return ret;
 }
-
-/**
- * kmsg_dump_get_line - retrieve one kmsg log line
- * @iter: kmsg dump iterator
- * @syslog: include the "<4>" prefixes
- * @line: buffer to copy the line to
- * @size: maximum size of the buffer
- * @len: length of line placed into buffer
- *
- * Start at the beginning of the kmsg buffer, with the oldest kmsg
- * record, and copy one record into the provided buffer.
- *
- * Consecutive calls will return the next available record moving
- * towards the end of the buffer with the youngest messages.
- *
- * A return value of FALSE indicates that there are no more records to
- * read.
- */
-bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
-			char *line, size_t size, size_t *len)
-{
-	unsigned long flags;
-	bool ret;
-
-	printk_safe_enter_irqsave(flags);
-	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
-	printk_safe_exit_irqrestore(flags);
-
-	return ret;
-}
 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
 
 /**
@@ -3542,22 +3513,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
 
-/**
- * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
- * @iter: kmsg dump iterator
- *
- * Reset the dumper's iterator so that kmsg_dump_get_line() and
- * kmsg_dump_get_buffer() can be called again and used multiple
- * times within the same dumper.dump() callback.
- *
- * The function is similar to kmsg_dump_rewind(), but grabs no locks.
- */
-void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
-{
-	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
-	iter->next_seq = prb_next_seq(prb);
-}
-
 /**
  * kmsg_dump_rewind - reset the iterator
  * @iter: kmsg dump iterator
@@ -3571,7 +3526,8 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 	unsigned long flags;
 
 	printk_safe_enter_irqsave(flags);
-	kmsg_dump_rewind_nolock(iter);
+	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
+	iter->next_seq = prb_next_seq(prb);
 	printk_safe_exit_irqrestore(flags);
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-- 
2.20.1

[PATCH next v3 15/15] printk: console: remove unnecessary safe buffer usage

[John Ogness]

Upon registering a console, safe buffers are activated when setting
up the sequence number to replay the log. However, these are already
protected by @console_sem and @syslog_lock. Remove the unnecessary
safe buffer usage.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 15a9bc409e0a..27a748ed0bc7 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2967,9 +2967,7 @@ void register_console(struct console *newcon)
 		/*
 		 * console_unlock(); will print out the buffered messages
 		 * for us.
-		 */
-		printk_safe_enter_irqsave(flags);
-		/*
+		 *
 		 * We're about to replay the log buffer.  Only do this to the
 		 * just-registered console to avoid excessive message spam to
 		 * the already-registered consoles.
@@ -2982,11 +2980,9 @@ void register_console(struct console *newcon)
 		exclusive_console_stop_seq = console_seq;
 
 		/* Get a consistent copy of @syslog_seq. */
-		raw_spin_lock(&syslog_lock);
+		raw_spin_lock_irqsave(&syslog_lock, flags);
 		console_seq = syslog_seq;
-		raw_spin_unlock(&syslog_lock);
-
-		printk_safe_exit_irqrestore(flags);
+		raw_spin_unlock_irqrestore(&syslog_lock, flags);
 	}
 	console_unlock();
 	console_sysfs_notify();
-- 
2.20.1

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Kees Cook]

On Thu, Feb 25, 2021 at 09:24:35PM +0100, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--

Reviewed-by: Kees Cook <keescook@chromium.org> # pstore

-Kees

>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     big_oops_buf, big_oops_buf_sz, &text_len);
>  		rc = zip_oops(text_len);
>  	}
>  	if (rc != 0) {
> -		kmsg_dump_rewind(dumper);
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     oops_data, oops_data_sz, &text_len);
>  		err_type = ERR_TYPE_KERNEL_PANIC;
>  		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
> diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
> index 6c3bc4b4da98..a7bd6ac681f4 100644
> --- a/arch/powerpc/platforms/powernv/opal-kmsg.c
> +++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
> @@ -19,8 +19,7 @@
>   * may not be completely printed.  This function does not actually dump the
>   * message, it just ensures that OPAL completely flushes the console buffer.
>   */
> -static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
> -				     enum kmsg_dump_reason reason)
> +static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
>  {
>  	/*
>  	 * Outside of a panic context the pollers will continue to run,
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 80ed3e1becf9..5978b90a885f 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
>  static void
>  dump_log_buf(void)
>  {
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	unsigned char buf[128];
>  	size_t len;
>  
> @@ -3013,9 +3013,9 @@ dump_log_buf(void)
>  	catch_memory_errors = 1;
>  	sync();
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> +	kmsg_dump_rewind_nolock(&iter);
>  	xmon_start_pagination();
> -	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
> +	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
>  		buf[len] = '\0';
>  		printf("%s", buf);
>  	}
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 4869e2cc787c..9fbc5e5b1023 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -7,9 +7,9 @@
>  #include <shared/kern.h>
>  #include <os.h>
>  
> -static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> -				enum kmsg_dump_reason reason)
> +static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
>  {
> +	static struct kmsg_dump_iter iter;
>  	static DEFINE_SPINLOCK(lock);
>  	static char line[1024];
>  	struct console *con;
> @@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  	if (!spin_trylock(&lock))
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	printf("kmsg_dump:\n");
> -	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
> +	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
>  		line[len] = '\0';
>  		printf("%s", line);
>  	}
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 10dce9f91216..1b858f280e22 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
>   * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
>   * buffer and call into Hyper-V to transfer the data.
>   */
> -static void hv_kmsg_dump(struct kmsg_dumper *dumper,
> -			 enum kmsg_dump_reason reason)
> +static void hv_kmsg_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	size_t bytes_written;
>  	phys_addr_t panic_pa;
>  
> @@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
>  	 * Write dump contents to the page. No need to synchronize; panic should
>  	 * be single-threaded.
>  	 */
> -	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
> +	kmsg_dump_rewind(&iter);
> +	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
>  			     &bytes_written);
>  	if (bytes_written)
>  		hyperv_report_panic_msg(panic_pa, bytes_written);
> diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> index 8bbfba40a554..d179b726a1c9 100644
> --- a/drivers/mtd/mtdoops.c
> +++ b/drivers/mtd/mtdoops.c
> @@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
>  	mtdoops_inc_counter(cxt);
>  }
>  
> -static void mtdoops_do_dump(struct kmsg_dumper *dumper,
> -			    enum kmsg_dump_reason reason)
> +static void mtdoops_do_dump(enum kmsg_dump_reason reason)
>  {
>  	struct mtdoops_context *cxt = container_of(dumper,
>  			struct mtdoops_context, dump);
> +	struct kmsg_dump_iter iter;
>  
>  	/* Only dump oopses if dump_oops is set */
>  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
>  		return;
> -	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> +	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
>  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
>  	clear_bit(0, &cxt->oops_buf_busy);
>  
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index d963ae7902f9..edfc9504e024 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
>   * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
>   * end of the buffer.
>   */
> -static void pstore_dump(struct kmsg_dumper *dumper,
> -			enum kmsg_dump_reason reason)
> +static void pstore_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	unsigned long	total = 0;
>  	const char	*why;
>  	unsigned int	part = 1;
> @@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		}
>  	}
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	oopscount++;
>  	while (total < kmsg_bytes) {
>  		char *dst;
> @@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		dst_size -= header_size;
>  
>  		/* Write dump contents. */
> -		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
> +		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
>  					  dst_size, &dump_size))
>  			break;
>  
> diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> index 84eaa2090efa..5d3bf20f9f0a 100644
> --- a/include/linux/kmsg_dump.h
> +++ b/include/linux/kmsg_dump.h
> @@ -29,6 +29,16 @@ enum kmsg_dump_reason {
>  	KMSG_DUMP_MAX
>  };
>  
> +/**
> + * struct kmsg_dump_iter - iterator for retrieving kernel messages
> + * @cur_seq:	Points to the oldest message to dump
> + * @next_seq:	Points after the newest message to dump
> + */
> +struct kmsg_dump_iter {
> +	u64	cur_seq;
> +	u64	next_seq;
> +};
> +
>  /**
>   * struct kmsg_dumper - kernel crash message dumper structure
>   * @list:	Entry in the dumper list (private)
> @@ -36,35 +46,29 @@ enum kmsg_dump_reason {
>   * 		through the record iterator
>   * @max_reason:	filter for highest reason number that should be dumped
>   * @registered:	Flag that specifies if this is already registered
> - * @cur_seq:	Points to the oldest message to dump
> - * @next_seq:	Points after the newest message to dump
>   */
>  struct kmsg_dumper {
>  	struct list_head list;
> -	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
> +	void (*dump)(enum kmsg_dump_reason reason);
>  	enum kmsg_dump_reason max_reason;
>  	bool registered;
> -
> -	/* private state of the kmsg iterator */
> -	u64 cur_seq;
> -	u64 next_seq;
>  };
>  
>  #ifdef CONFIG_PRINTK
>  void kmsg_dump(enum kmsg_dump_reason reason);
>  
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out);
>  
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
>  
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
>  
>  int kmsg_dump_register(struct kmsg_dumper *dumper);
>  
> @@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  }
>  
> -static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
> +static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
>  					     bool syslog, const char *line,
>  					     size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  				const char *line, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  					char *buf, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> -static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 315169d5e119..8544d7a55a57 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
>  	int adjust = 0;
>  	int n = 0;
>  	int skip = 0;
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	size_t len;
>  	char buf[201];
>  
> @@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  		kdb_set(2, setargs);
>  	}
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
>  		n++;
>  
>  	if (lines < 0) {
> @@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  	if (skip >= n || skip < 0)
>  		return 0;
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
>  		if (skip) {
>  			skip--;
>  			continue;
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 45cb3e9c62c5..e58ccc368348 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
>  void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  	struct kmsg_dumper *dumper;
> -	unsigned long flags;
>  
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(dumper, &dump_list, list) {
> @@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>  		if (reason > max_reason)
>  			continue;
>  
> -		/* initialize iterator with data about the stored records */
> -		logbuf_lock_irqsave(flags);
> -		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -		dumper->next_seq = prb_next_seq(prb);
> -		logbuf_unlock_irqrestore(flags);
> -
>  		/* invoke dumper which will iterate over records */
> -		dumper->dump(dumper, reason);
> +		dumper->dump(reason);
>  	}
>  	rcu_read_unlock();
>  }
>  
>  /**
>   * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>   *
>   * The function is similar to kmsg_dump_get_line(), but grabs no locks.
>   */
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len)
>  {
>  	struct printk_info info;
> @@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	/* Read text or count text lines? */
>  	if (line) {
> -		if (!prb_read_valid(prb, dumper->cur_seq, &r))
> +		if (!prb_read_valid(prb, iter->cur_seq, &r))
>  			goto out;
>  		l = record_print_text(&r, syslog, printk_time);
>  	} else {
> -		if (!prb_read_valid_info(prb, dumper->cur_seq,
> +		if (!prb_read_valid_info(prb, iter->cur_seq,
>  					 &info, &line_count)) {
>  			goto out;
>  		}
> @@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	}
>  
> -	dumper->cur_seq = r.info->seq + 1;
> +	iter->cur_seq = r.info->seq + 1;
>  	ret = true;
>  out:
>  	if (len)
> @@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  /**
>   * kmsg_dump_get_line - retrieve one kmsg log line
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len)
>  {
>  	unsigned long flags;
>  	bool ret;
>  
>  	logbuf_lock_irqsave(flags);
> -	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
> +	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
>  	logbuf_unlock_irqrestore(flags);
>  
>  	return ret;
> @@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>  
>  /**
>   * kmsg_dump_get_buffer - copy kmsg log lines
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @buf: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out)
>  {
>  	struct printk_info info;
> @@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		goto out;
>  
>  	logbuf_lock_irqsave(flags);
> -	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
> -		if (info.seq != dumper->cur_seq) {
> +	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
> +		if (info.seq != iter->cur_seq) {
>  			/* messages are gone, move to first available one */
> -			dumper->cur_seq = info.seq;
> +			iter->cur_seq = info.seq;
>  		}
>  	}
>  
>  	/* last entry */
> -	if (dumper->cur_seq >= dumper->next_seq) {
> +	if (iter->cur_seq >= iter->next_seq) {
>  		logbuf_unlock_irqrestore(flags);
>  		goto out;
>  	}
> @@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  	 * because this function (by way of record_print_text()) will
>  	 * not write more than size-1 bytes of text into @buf.
>  	 */
> -	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
> +	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
>  				     size - 1, syslog, time);
>  
>  	/*
> @@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  
>  	len = 0;
>  	prb_for_each_record(seq, prb, seq, &r) {
> -		if (r.info->seq >= dumper->next_seq)
> +		if (r.info->seq >= iter->next_seq)
>  			break;
>  
>  		len += record_print_text(&r, syslog, time);
> @@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		prb_rec_init_rd(&r, &info, buf + len, size - len);
>  	}
>  
> -	dumper->next_seq = next_seq;
> +	iter->next_seq = next_seq;
>  	ret = true;
>  	logbuf_unlock_irqrestore(flags);
>  out:
> @@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>  
>  /**
>   * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
> @@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>   *
>   * The function is similar to kmsg_dump_rewind(), but grabs no locks.
>   */
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
> -	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -	dumper->next_seq = prb_next_seq(prb);
> +	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
> +	iter->next_seq = prb_next_seq(prb);
>  }
>  
>  /**
>   * kmsg_dump_rewind - reset the iterator
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
>   * times within the same dumper.dump() callback.
>   */
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  	unsigned long flags;
>  
>  	logbuf_lock_irqsave(flags);
> -	kmsg_dump_rewind_nolock(dumper);
> +	kmsg_dump_rewind_nolock(iter);
>  	logbuf_unlock_irqrestore(flags);
>  }
>  EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
> -- 
> 2.20.1
> 

-- 
Kees Cook

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Kees Cook]

On Thu, Feb 25, 2021 at 09:24:35PM +0100, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--

Reviewed-by: Kees Cook <keescook@chromium.org> # pstore

-Kees

>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     big_oops_buf, big_oops_buf_sz, &text_len);
>  		rc = zip_oops(text_len);
>  	}
>  	if (rc != 0) {
> -		kmsg_dump_rewind(dumper);
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     oops_data, oops_data_sz, &text_len);
>  		err_type = ERR_TYPE_KERNEL_PANIC;
>  		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
> diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
> index 6c3bc4b4da98..a7bd6ac681f4 100644
> --- a/arch/powerpc/platforms/powernv/opal-kmsg.c
> +++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
> @@ -19,8 +19,7 @@
>   * may not be completely printed.  This function does not actually dump the
>   * message, it just ensures that OPAL completely flushes the console buffer.
>   */
> -static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
> -				     enum kmsg_dump_reason reason)
> +static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
>  {
>  	/*
>  	 * Outside of a panic context the pollers will continue to run,
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 80ed3e1becf9..5978b90a885f 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
>  static void
>  dump_log_buf(void)
>  {
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	unsigned char buf[128];
>  	size_t len;
>  
> @@ -3013,9 +3013,9 @@ dump_log_buf(void)
>  	catch_memory_errors = 1;
>  	sync();
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> +	kmsg_dump_rewind_nolock(&iter);
>  	xmon_start_pagination();
> -	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
> +	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
>  		buf[len] = '\0';
>  		printf("%s", buf);
>  	}
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 4869e2cc787c..9fbc5e5b1023 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -7,9 +7,9 @@
>  #include <shared/kern.h>
>  #include <os.h>
>  
> -static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> -				enum kmsg_dump_reason reason)
> +static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
>  {
> +	static struct kmsg_dump_iter iter;
>  	static DEFINE_SPINLOCK(lock);
>  	static char line[1024];
>  	struct console *con;
> @@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  	if (!spin_trylock(&lock))
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	printf("kmsg_dump:\n");
> -	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
> +	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
>  		line[len] = '\0';
>  		printf("%s", line);
>  	}
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 10dce9f91216..1b858f280e22 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
>   * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
>   * buffer and call into Hyper-V to transfer the data.
>   */
> -static void hv_kmsg_dump(struct kmsg_dumper *dumper,
> -			 enum kmsg_dump_reason reason)
> +static void hv_kmsg_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	size_t bytes_written;
>  	phys_addr_t panic_pa;
>  
> @@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
>  	 * Write dump contents to the page. No need to synchronize; panic should
>  	 * be single-threaded.
>  	 */
> -	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
> +	kmsg_dump_rewind(&iter);
> +	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
>  			     &bytes_written);
>  	if (bytes_written)
>  		hyperv_report_panic_msg(panic_pa, bytes_written);
> diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> index 8bbfba40a554..d179b726a1c9 100644
> --- a/drivers/mtd/mtdoops.c
> +++ b/drivers/mtd/mtdoops.c
> @@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
>  	mtdoops_inc_counter(cxt);
>  }
>  
> -static void mtdoops_do_dump(struct kmsg_dumper *dumper,
> -			    enum kmsg_dump_reason reason)
> +static void mtdoops_do_dump(enum kmsg_dump_reason reason)
>  {
>  	struct mtdoops_context *cxt = container_of(dumper,
>  			struct mtdoops_context, dump);
> +	struct kmsg_dump_iter iter;
>  
>  	/* Only dump oopses if dump_oops is set */
>  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
>  		return;
> -	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> +	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
>  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
>  	clear_bit(0, &cxt->oops_buf_busy);
>  
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index d963ae7902f9..edfc9504e024 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
>   * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
>   * end of the buffer.
>   */
> -static void pstore_dump(struct kmsg_dumper *dumper,
> -			enum kmsg_dump_reason reason)
> +static void pstore_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	unsigned long	total = 0;
>  	const char	*why;
>  	unsigned int	part = 1;
> @@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		}
>  	}
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	oopscount++;
>  	while (total < kmsg_bytes) {
>  		char *dst;
> @@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		dst_size -= header_size;
>  
>  		/* Write dump contents. */
> -		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
> +		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
>  					  dst_size, &dump_size))
>  			break;
>  
> diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> index 84eaa2090efa..5d3bf20f9f0a 100644
> --- a/include/linux/kmsg_dump.h
> +++ b/include/linux/kmsg_dump.h
> @@ -29,6 +29,16 @@ enum kmsg_dump_reason {
>  	KMSG_DUMP_MAX
>  };
>  
> +/**
> + * struct kmsg_dump_iter - iterator for retrieving kernel messages
> + * @cur_seq:	Points to the oldest message to dump
> + * @next_seq:	Points after the newest message to dump
> + */
> +struct kmsg_dump_iter {
> +	u64	cur_seq;
> +	u64	next_seq;
> +};
> +
>  /**
>   * struct kmsg_dumper - kernel crash message dumper structure
>   * @list:	Entry in the dumper list (private)
> @@ -36,35 +46,29 @@ enum kmsg_dump_reason {
>   * 		through the record iterator
>   * @max_reason:	filter for highest reason number that should be dumped
>   * @registered:	Flag that specifies if this is already registered
> - * @cur_seq:	Points to the oldest message to dump
> - * @next_seq:	Points after the newest message to dump
>   */
>  struct kmsg_dumper {
>  	struct list_head list;
> -	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
> +	void (*dump)(enum kmsg_dump_reason reason);
>  	enum kmsg_dump_reason max_reason;
>  	bool registered;
> -
> -	/* private state of the kmsg iterator */
> -	u64 cur_seq;
> -	u64 next_seq;
>  };
>  
>  #ifdef CONFIG_PRINTK
>  void kmsg_dump(enum kmsg_dump_reason reason);
>  
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out);
>  
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
>  
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
>  
>  int kmsg_dump_register(struct kmsg_dumper *dumper);
>  
> @@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  }
>  
> -static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
> +static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
>  					     bool syslog, const char *line,
>  					     size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  				const char *line, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  					char *buf, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> -static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 315169d5e119..8544d7a55a57 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
>  	int adjust = 0;
>  	int n = 0;
>  	int skip = 0;
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	size_t len;
>  	char buf[201];
>  
> @@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  		kdb_set(2, setargs);
>  	}
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
>  		n++;
>  
>  	if (lines < 0) {
> @@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  	if (skip >= n || skip < 0)
>  		return 0;
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
>  		if (skip) {
>  			skip--;
>  			continue;
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 45cb3e9c62c5..e58ccc368348 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
>  void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  	struct kmsg_dumper *dumper;
> -	unsigned long flags;
>  
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(dumper, &dump_list, list) {
> @@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>  		if (reason > max_reason)
>  			continue;
>  
> -		/* initialize iterator with data about the stored records */
> -		logbuf_lock_irqsave(flags);
> -		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -		dumper->next_seq = prb_next_seq(prb);
> -		logbuf_unlock_irqrestore(flags);
> -
>  		/* invoke dumper which will iterate over records */
> -		dumper->dump(dumper, reason);
> +		dumper->dump(reason);
>  	}
>  	rcu_read_unlock();
>  }
>  
>  /**
>   * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>   *
>   * The function is similar to kmsg_dump_get_line(), but grabs no locks.
>   */
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len)
>  {
>  	struct printk_info info;
> @@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	/* Read text or count text lines? */
>  	if (line) {
> -		if (!prb_read_valid(prb, dumper->cur_seq, &r))
> +		if (!prb_read_valid(prb, iter->cur_seq, &r))
>  			goto out;
>  		l = record_print_text(&r, syslog, printk_time);
>  	} else {
> -		if (!prb_read_valid_info(prb, dumper->cur_seq,
> +		if (!prb_read_valid_info(prb, iter->cur_seq,
>  					 &info, &line_count)) {
>  			goto out;
>  		}
> @@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	}
>  
> -	dumper->cur_seq = r.info->seq + 1;
> +	iter->cur_seq = r.info->seq + 1;
>  	ret = true;
>  out:
>  	if (len)
> @@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  /**
>   * kmsg_dump_get_line - retrieve one kmsg log line
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len)
>  {
>  	unsigned long flags;
>  	bool ret;
>  
>  	logbuf_lock_irqsave(flags);
> -	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
> +	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
>  	logbuf_unlock_irqrestore(flags);
>  
>  	return ret;
> @@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>  
>  /**
>   * kmsg_dump_get_buffer - copy kmsg log lines
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @buf: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out)
>  {
>  	struct printk_info info;
> @@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		goto out;
>  
>  	logbuf_lock_irqsave(flags);
> -	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
> -		if (info.seq != dumper->cur_seq) {
> +	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
> +		if (info.seq != iter->cur_seq) {
>  			/* messages are gone, move to first available one */
> -			dumper->cur_seq = info.seq;
> +			iter->cur_seq = info.seq;
>  		}
>  	}
>  
>  	/* last entry */
> -	if (dumper->cur_seq >= dumper->next_seq) {
> +	if (iter->cur_seq >= iter->next_seq) {
>  		logbuf_unlock_irqrestore(flags);
>  		goto out;
>  	}
> @@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  	 * because this function (by way of record_print_text()) will
>  	 * not write more than size-1 bytes of text into @buf.
>  	 */
> -	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
> +	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
>  				     size - 1, syslog, time);
>  
>  	/*
> @@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  
>  	len = 0;
>  	prb_for_each_record(seq, prb, seq, &r) {
> -		if (r.info->seq >= dumper->next_seq)
> +		if (r.info->seq >= iter->next_seq)
>  			break;
>  
>  		len += record_print_text(&r, syslog, time);
> @@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		prb_rec_init_rd(&r, &info, buf + len, size - len);
>  	}
>  
> -	dumper->next_seq = next_seq;
> +	iter->next_seq = next_seq;
>  	ret = true;
>  	logbuf_unlock_irqrestore(flags);
>  out:
> @@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>  
>  /**
>   * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
> @@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>   *
>   * The function is similar to kmsg_dump_rewind(), but grabs no locks.
>   */
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
> -	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -	dumper->next_seq = prb_next_seq(prb);
> +	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
> +	iter->next_seq = prb_next_seq(prb);
>  }
>  
>  /**
>   * kmsg_dump_rewind - reset the iterator
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
>   * times within the same dumper.dump() callback.
>   */
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  	unsigned long flags;
>  
>  	logbuf_lock_irqsave(flags);
> -	kmsg_dump_rewind_nolock(dumper);
> +	kmsg_dump_rewind_nolock(iter);
>  	logbuf_unlock_irqrestore(flags);
>  }
>  EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
> -- 
> 2.20.1
> 

-- 
Kees Cook

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Kees Cook]

On Thu, Feb 25, 2021 at 09:24:35PM +0100, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--

Reviewed-by: Kees Cook <keescook@chromium.org> # pstore

-Kees

>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     big_oops_buf, big_oops_buf_sz, &text_len);
>  		rc = zip_oops(text_len);
>  	}
>  	if (rc != 0) {
> -		kmsg_dump_rewind(dumper);
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);
> +		kmsg_dump_get_buffer(&iter, false,
>  				     oops_data, oops_data_sz, &text_len);
>  		err_type = ERR_TYPE_KERNEL_PANIC;
>  		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);
> diff --git a/arch/powerpc/platforms/powernv/opal-kmsg.c b/arch/powerpc/platforms/powernv/opal-kmsg.c
> index 6c3bc4b4da98..a7bd6ac681f4 100644
> --- a/arch/powerpc/platforms/powernv/opal-kmsg.c
> +++ b/arch/powerpc/platforms/powernv/opal-kmsg.c
> @@ -19,8 +19,7 @@
>   * may not be completely printed.  This function does not actually dump the
>   * message, it just ensures that OPAL completely flushes the console buffer.
>   */
> -static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
> -				     enum kmsg_dump_reason reason)
> +static void kmsg_dump_opal_console_flush(enum kmsg_dump_reason reason)
>  {
>  	/*
>  	 * Outside of a panic context the pollers will continue to run,
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 80ed3e1becf9..5978b90a885f 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
>  static void
>  dump_log_buf(void)
>  {
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	unsigned char buf[128];
>  	size_t len;
>  
> @@ -3013,9 +3013,9 @@ dump_log_buf(void)
>  	catch_memory_errors = 1;
>  	sync();
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> +	kmsg_dump_rewind_nolock(&iter);
>  	xmon_start_pagination();
> -	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
> +	while (kmsg_dump_get_line_nolock(&iter, false, buf, sizeof(buf), &len)) {
>  		buf[len] = '\0';
>  		printf("%s", buf);
>  	}
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 4869e2cc787c..9fbc5e5b1023 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -7,9 +7,9 @@
>  #include <shared/kern.h>
>  #include <os.h>
>  
> -static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> -				enum kmsg_dump_reason reason)
> +static void kmsg_dumper_stdout(enum kmsg_dump_reason reason)
>  {
> +	static struct kmsg_dump_iter iter;
>  	static DEFINE_SPINLOCK(lock);
>  	static char line[1024];
>  	struct console *con;
> @@ -34,8 +34,10 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  	if (!spin_trylock(&lock))
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	printf("kmsg_dump:\n");
> -	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
> +	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
>  		line[len] = '\0';
>  		printf("%s", line);
>  	}
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 10dce9f91216..1b858f280e22 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1388,9 +1388,9 @@ static void vmbus_isr(void)
>   * Callback from kmsg_dump. Grab as much as possible from the end of the kmsg
>   * buffer and call into Hyper-V to transfer the data.
>   */
> -static void hv_kmsg_dump(struct kmsg_dumper *dumper,
> -			 enum kmsg_dump_reason reason)
> +static void hv_kmsg_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	size_t bytes_written;
>  	phys_addr_t panic_pa;
>  
> @@ -1404,7 +1404,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
>  	 * Write dump contents to the page. No need to synchronize; panic should
>  	 * be single-threaded.
>  	 */
> -	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
> +	kmsg_dump_rewind(&iter);
> +	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
>  			     &bytes_written);
>  	if (bytes_written)
>  		hyperv_report_panic_msg(panic_pa, bytes_written);
> diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> index 8bbfba40a554..d179b726a1c9 100644
> --- a/drivers/mtd/mtdoops.c
> +++ b/drivers/mtd/mtdoops.c
> @@ -272,19 +272,21 @@ static void find_next_position(struct mtdoops_context *cxt)
>  	mtdoops_inc_counter(cxt);
>  }
>  
> -static void mtdoops_do_dump(struct kmsg_dumper *dumper,
> -			    enum kmsg_dump_reason reason)
> +static void mtdoops_do_dump(enum kmsg_dump_reason reason)
>  {
>  	struct mtdoops_context *cxt = container_of(dumper,
>  			struct mtdoops_context, dump);
> +	struct kmsg_dump_iter iter;
>  
>  	/* Only dump oopses if dump_oops is set */
>  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
>  		return;
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
>  		return;
> -	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> +	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
>  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
>  	clear_bit(0, &cxt->oops_buf_busy);
>  
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index d963ae7902f9..edfc9504e024 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -382,9 +382,9 @@ void pstore_record_init(struct pstore_record *record,
>   * callback from kmsg_dump. Save as much as we can (up to kmsg_bytes) from the
>   * end of the buffer.
>   */
> -static void pstore_dump(struct kmsg_dumper *dumper,
> -			enum kmsg_dump_reason reason)
> +static void pstore_dump(enum kmsg_dump_reason reason)
>  {
> +	struct kmsg_dump_iter iter;
>  	unsigned long	total = 0;
>  	const char	*why;
>  	unsigned int	part = 1;
> @@ -405,6 +405,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		}
>  	}
>  
> +	kmsg_dump_rewind(&iter);
> +
>  	oopscount++;
>  	while (total < kmsg_bytes) {
>  		char *dst;
> @@ -435,7 +437,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
>  		dst_size -= header_size;
>  
>  		/* Write dump contents. */
> -		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
> +		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
>  					  dst_size, &dump_size))
>  			break;
>  
> diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> index 84eaa2090efa..5d3bf20f9f0a 100644
> --- a/include/linux/kmsg_dump.h
> +++ b/include/linux/kmsg_dump.h
> @@ -29,6 +29,16 @@ enum kmsg_dump_reason {
>  	KMSG_DUMP_MAX
>  };
>  
> +/**
> + * struct kmsg_dump_iter - iterator for retrieving kernel messages
> + * @cur_seq:	Points to the oldest message to dump
> + * @next_seq:	Points after the newest message to dump
> + */
> +struct kmsg_dump_iter {
> +	u64	cur_seq;
> +	u64	next_seq;
> +};
> +
>  /**
>   * struct kmsg_dumper - kernel crash message dumper structure
>   * @list:	Entry in the dumper list (private)
> @@ -36,35 +46,29 @@ enum kmsg_dump_reason {
>   * 		through the record iterator
>   * @max_reason:	filter for highest reason number that should be dumped
>   * @registered:	Flag that specifies if this is already registered
> - * @cur_seq:	Points to the oldest message to dump
> - * @next_seq:	Points after the newest message to dump
>   */
>  struct kmsg_dumper {
>  	struct list_head list;
> -	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
> +	void (*dump)(enum kmsg_dump_reason reason);
>  	enum kmsg_dump_reason max_reason;
>  	bool registered;
> -
> -	/* private state of the kmsg iterator */
> -	u64 cur_seq;
> -	u64 next_seq;
>  };
>  
>  #ifdef CONFIG_PRINTK
>  void kmsg_dump(enum kmsg_dump_reason reason);
>  
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len);
>  
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out);
>  
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
>  
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper);
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
>  
>  int kmsg_dump_register(struct kmsg_dumper *dumper);
>  
> @@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  }
>  
> -static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
> +static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
>  					     bool syslog, const char *line,
>  					     size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  				const char *line, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  					char *buf, size_t size, size_t *len)
>  {
>  	return false;
>  }
>  
> -static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> -static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  }
>  
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 315169d5e119..8544d7a55a57 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -2101,7 +2101,7 @@ static int kdb_dmesg(int argc, const char **argv)
>  	int adjust = 0;
>  	int n = 0;
>  	int skip = 0;
> -	struct kmsg_dumper dumper;
> +	struct kmsg_dump_iter iter;
>  	size_t len;
>  	char buf[201];
>  
> @@ -2126,8 +2126,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  		kdb_set(2, setargs);
>  	}
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, NULL, 0, NULL))
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, NULL, 0, NULL))
>  		n++;
>  
>  	if (lines < 0) {
> @@ -2159,8 +2159,8 @@ static int kdb_dmesg(int argc, const char **argv)
>  	if (skip >= n || skip < 0)
>  		return 0;
>  
> -	kmsg_dump_rewind_nolock(&dumper);
> -	while (kmsg_dump_get_line_nolock(&dumper, 1, buf, sizeof(buf), &len)) {
> +	kmsg_dump_rewind_nolock(&iter);
> +	while (kmsg_dump_get_line_nolock(&iter, 1, buf, sizeof(buf), &len)) {
>  		if (skip) {
>  			skip--;
>  			continue;
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 45cb3e9c62c5..e58ccc368348 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3390,7 +3390,6 @@ EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
>  void kmsg_dump(enum kmsg_dump_reason reason)
>  {
>  	struct kmsg_dumper *dumper;
> -	unsigned long flags;
>  
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(dumper, &dump_list, list) {
> @@ -3407,21 +3406,15 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>  		if (reason > max_reason)
>  			continue;
>  
> -		/* initialize iterator with data about the stored records */
> -		logbuf_lock_irqsave(flags);
> -		dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -		dumper->next_seq = prb_next_seq(prb);
> -		logbuf_unlock_irqrestore(flags);
> -
>  		/* invoke dumper which will iterate over records */
> -		dumper->dump(dumper, reason);
> +		dumper->dump(reason);
>  	}
>  	rcu_read_unlock();
>  }
>  
>  /**
>   * kmsg_dump_get_line_nolock - retrieve one kmsg log line (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3438,7 +3431,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
>   *
>   * The function is similar to kmsg_dump_get_line(), but grabs no locks.
>   */
> -bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
>  			       char *line, size_t size, size_t *len)
>  {
>  	struct printk_info info;
> @@ -3451,11 +3444,11 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	/* Read text or count text lines? */
>  	if (line) {
> -		if (!prb_read_valid(prb, dumper->cur_seq, &r))
> +		if (!prb_read_valid(prb, iter->cur_seq, &r))
>  			goto out;
>  		l = record_print_text(&r, syslog, printk_time);
>  	} else {
> -		if (!prb_read_valid_info(prb, dumper->cur_seq,
> +		if (!prb_read_valid_info(prb, iter->cur_seq,
>  					 &info, &line_count)) {
>  			goto out;
>  		}
> @@ -3464,7 +3457,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  	}
>  
> -	dumper->cur_seq = r.info->seq + 1;
> +	iter->cur_seq = r.info->seq + 1;
>  	ret = true;
>  out:
>  	if (len)
> @@ -3474,7 +3467,7 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>  
>  /**
>   * kmsg_dump_get_line - retrieve one kmsg log line
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @line: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3489,14 +3482,14 @@ bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
>  			char *line, size_t size, size_t *len)
>  {
>  	unsigned long flags;
>  	bool ret;
>  
>  	logbuf_lock_irqsave(flags);
> -	ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
> +	ret = kmsg_dump_get_line_nolock(iter, syslog, line, size, len);
>  	logbuf_unlock_irqrestore(flags);
>  
>  	return ret;
> @@ -3505,7 +3498,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>  
>  /**
>   * kmsg_dump_get_buffer - copy kmsg log lines
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   * @syslog: include the "<4>" prefixes
>   * @buf: buffer to copy the line to
>   * @size: maximum size of the buffer
> @@ -3522,7 +3515,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
>   * A return value of FALSE indicates that there are no more records to
>   * read.
>   */
> -bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
> +bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
>  			  char *buf, size_t size, size_t *len_out)
>  {
>  	struct printk_info info;
> @@ -3538,15 +3531,15 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		goto out;
>  
>  	logbuf_lock_irqsave(flags);
> -	if (prb_read_valid_info(prb, dumper->cur_seq, &info, NULL)) {
> -		if (info.seq != dumper->cur_seq) {
> +	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
> +		if (info.seq != iter->cur_seq) {
>  			/* messages are gone, move to first available one */
> -			dumper->cur_seq = info.seq;
> +			iter->cur_seq = info.seq;
>  		}
>  	}
>  
>  	/* last entry */
> -	if (dumper->cur_seq >= dumper->next_seq) {
> +	if (iter->cur_seq >= iter->next_seq) {
>  		logbuf_unlock_irqrestore(flags);
>  		goto out;
>  	}
> @@ -3557,7 +3550,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  	 * because this function (by way of record_print_text()) will
>  	 * not write more than size-1 bytes of text into @buf.
>  	 */
> -	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
> +	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
>  				     size - 1, syslog, time);
>  
>  	/*
> @@ -3570,7 +3563,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  
>  	len = 0;
>  	prb_for_each_record(seq, prb, seq, &r) {
> -		if (r.info->seq >= dumper->next_seq)
> +		if (r.info->seq >= iter->next_seq)
>  			break;
>  
>  		len += record_print_text(&r, syslog, time);
> @@ -3579,7 +3572,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
>  		prb_rec_init_rd(&r, &info, buf + len, size - len);
>  	}
>  
> -	dumper->next_seq = next_seq;
> +	iter->next_seq = next_seq;
>  	ret = true;
>  	logbuf_unlock_irqrestore(flags);
>  out:
> @@ -3591,7 +3584,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>  
>  /**
>   * kmsg_dump_rewind_nolock - reset the iterator (unlocked version)
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
> @@ -3599,26 +3592,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
>   *
>   * The function is similar to kmsg_dump_rewind(), but grabs no locks.
>   */
> -void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
>  {
> -	dumper->cur_seq = latched_seq_read_nolock(&clear_seq);
> -	dumper->next_seq = prb_next_seq(prb);
> +	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
> +	iter->next_seq = prb_next_seq(prb);
>  }
>  
>  /**
>   * kmsg_dump_rewind - reset the iterator
> - * @dumper: registered kmsg dumper
> + * @iter: kmsg dump iterator
>   *
>   * Reset the dumper's iterator so that kmsg_dump_get_line() and
>   * kmsg_dump_get_buffer() can be called again and used multiple
>   * times within the same dumper.dump() callback.
>   */
> -void kmsg_dump_rewind(struct kmsg_dumper *dumper)
> +void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
>  {
>  	unsigned long flags;
>  
>  	logbuf_lock_irqsave(flags);
> -	kmsg_dump_rewind_nolock(dumper);
> +	kmsg_dump_rewind_nolock(iter);
>  	logbuf_unlock_irqrestore(flags);
>  }
>  EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
> -- 
> 2.20.1
> 

-- 
Kees Cook

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[kernel test robot]

[-- Attachment #1: Type: text/plain, Size: 3957 bytes --]

Hi John,

I love your patch! Yet something to improve:

[auto build test ERROR on next-20210225]

url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
config: arm-randconfig-r024-20210225 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install arm cross compiling tool for clang build
        # apt-get install binutils-arm-linux-gnueabi
        # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
        git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
           struct mtdoops_context *cxt = container_of(dumper,
                                                      ^
>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
   3 errors generated.


vim +/dumper +277 drivers/mtd/mtdoops.c

4b23aff083649e Richard Purdie 2007-05-29  274  
fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
fc7f655cded40f John Ogness    2021-02-25  286  
df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
df92cad8a03e83 John Ogness    2021-02-25  288  		return;
fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
4b23aff083649e Richard Purdie 2007-05-29  301  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

[-- Attachment #2: config.gz --]
[-- Type: application/gzip, Size: 30841 bytes --]

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Hello,

Thank you kernel test robot!

Despite all of my efforts to carefully construct and test this series,
somehome I managed to miss a compile test with CONFIG_MTD_OOPS. That
kmsg_dumper does require the dumper parameter so that it can use
container_of().

I will discuss this with the printk team. But most likely we will just
re-instate the dumper parameter in the callback.

I apologize for the lack of care on my part.

John Ogness

On 2021-02-26, kernel test robot <lkp@intel.com> wrote:
> Hi John,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on next-20210225]
>
> url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
> base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
> config: arm-randconfig-r024-20210225 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
>         git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>            struct mtdoops_context *cxt = container_of(dumper,
>                                                       ^
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>    3 errors generated.
>
>
> vim +/dumper +277 drivers/mtd/mtdoops.c
>
> 4b23aff083649e Richard Purdie 2007-05-29  274  
> fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
> fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
> fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
> fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
> fc7f655cded40f John Ogness    2021-02-25  286  
> df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
> df92cad8a03e83 John Ogness    2021-02-25  288  		return;
> fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
> df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
> 4b23aff083649e Richard Purdie 2007-05-29  301  
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Hello,

Thank you kernel test robot!

Despite all of my efforts to carefully construct and test this series,
somehome I managed to miss a compile test with CONFIG_MTD_OOPS. That
kmsg_dumper does require the dumper parameter so that it can use
container_of().

I will discuss this with the printk team. But most likely we will just
re-instate the dumper parameter in the callback.

I apologize for the lack of care on my part.

John Ogness

On 2021-02-26, kernel test robot <lkp@intel.com> wrote:
> Hi John,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on next-20210225]
>
> url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
> base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
> config: arm-randconfig-r024-20210225 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
>         git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>            struct mtdoops_context *cxt = container_of(dumper,
>                                                       ^
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>    3 errors generated.
>
>
> vim +/dumper +277 drivers/mtd/mtdoops.c
>
> 4b23aff083649e Richard Purdie 2007-05-29  274  
> fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
> fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
> fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
> fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
> fc7f655cded40f John Ogness    2021-02-25  286  
> df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
> df92cad8a03e83 John Ogness    2021-02-25  288  		return;
> fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
> df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
> 4b23aff083649e Richard Purdie 2007-05-29  301  
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Hello,

Thank you kernel test robot!

Despite all of my efforts to carefully construct and test this series,
somehome I managed to miss a compile test with CONFIG_MTD_OOPS. That
kmsg_dumper does require the dumper parameter so that it can use
container_of().

I will discuss this with the printk team. But most likely we will just
re-instate the dumper parameter in the callback.

I apologize for the lack of care on my part.

John Ogness

On 2021-02-26, kernel test robot <lkp@intel.com> wrote:
> Hi John,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on next-20210225]
>
> url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
> base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
> config: arm-randconfig-r024-20210225 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
>         git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>            struct mtdoops_context *cxt = container_of(dumper,
>                                                       ^
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>    3 errors generated.
>
>
> vim +/dumper +277 drivers/mtd/mtdoops.c
>
> 4b23aff083649e Richard Purdie 2007-05-29  274  
> fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
> fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
> fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
> fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
> fc7f655cded40f John Ogness    2021-02-25  286  
> df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
> df92cad8a03e83 John Ogness    2021-02-25  288  		return;
> fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
> df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
> 4b23aff083649e Richard Purdie 2007-05-29  301  
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

[-- Attachment #1: Type: text/plain, Size: 4593 bytes --]

Hello,

Thank you kernel test robot!

Despite all of my efforts to carefully construct and test this series,
somehome I managed to miss a compile test with CONFIG_MTD_OOPS. That
kmsg_dumper does require the dumper parameter so that it can use
container_of().

I will discuss this with the printk team. But most likely we will just
re-instate the dumper parameter in the callback.

I apologize for the lack of care on my part.

John Ogness

On 2021-02-26, kernel test robot <lkp@intel.com> wrote:
> Hi John,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on next-20210225]
>
> url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
> base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
> config: arm-randconfig-r024-20210225 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
>         git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>            struct mtdoops_context *cxt = container_of(dumper,
>                                                       ^
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>    3 errors generated.
>
>
> vim +/dumper +277 drivers/mtd/mtdoops.c
>
> 4b23aff083649e Richard Purdie 2007-05-29  274  
> fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
> fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
> fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
> fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
> fc7f655cded40f John Ogness    2021-02-25  286  
> df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
> df92cad8a03e83 John Ogness    2021-02-25  288  		return;
> fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
> df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
> 4b23aff083649e Richard Purdie 2007-05-29  301  
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

Hello,

Thank you kernel test robot!

Despite all of my efforts to carefully construct and test this series,
somehome I managed to miss a compile test with CONFIG_MTD_OOPS. That
kmsg_dumper does require the dumper parameter so that it can use
container_of().

I will discuss this with the printk team. But most likely we will just
re-instate the dumper parameter in the callback.

I apologize for the lack of care on my part.

John Ogness

On 2021-02-26, kernel test robot <lkp@intel.com> wrote:
> Hi John,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on next-20210225]
>
> url:    https://github.com/0day-ci/linux/commits/John-Ogness/printk-remove-logbuf_lock/20210226-043457
> base:    7f206cf3ec2bee4621325cfacb2588e5085c07f5
> config: arm-randconfig-r024-20210225 (attached as .config)
> compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project a921aaf789912d981cbb2036bdc91ad7289e1523)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # install arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://github.com/0day-ci/linux/commit/fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         git remote add linux-review https://github.com/0day-ci/linux
>         git fetch --no-tags linux-review John-Ogness/printk-remove-logbuf_lock/20210226-043457
>         git checkout fc7f655cded40fc98ba5304c200e3a01e8291fb4
>         # save the attached .config to linux build tree
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm 
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>            struct mtdoops_context *cxt = container_of(dumper,
>                                                       ^
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>>> drivers/mtd/mtdoops.c:277:45: error: use of undeclared identifier 'dumper'
>    3 errors generated.
>
>
> vim +/dumper +277 drivers/mtd/mtdoops.c
>
> 4b23aff083649e Richard Purdie 2007-05-29  274  
> fc7f655cded40f John Ogness    2021-02-25  275  static void mtdoops_do_dump(enum kmsg_dump_reason reason)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  276  {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03 @277  	struct mtdoops_context *cxt = container_of(dumper,
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  278  			struct mtdoops_context, dump);
> fc7f655cded40f John Ogness    2021-02-25  279  	struct kmsg_dump_iter iter;
> fc2d557c74dc58 Seiji Aguchi   2011-01-12  280  
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  281  	/* Only dump oopses if dump_oops is set */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  282  	if (reason == KMSG_DUMP_OOPS && !dump_oops)
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  283  		return;
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  284  
> fc7f655cded40f John Ogness    2021-02-25  285  	kmsg_dump_rewind(&iter);
> fc7f655cded40f John Ogness    2021-02-25  286  
> df92cad8a03e83 John Ogness    2021-02-25  287  	if (test_and_set_bit(0, &cxt->oops_buf_busy))
> df92cad8a03e83 John Ogness    2021-02-25  288  		return;
> fc7f655cded40f John Ogness    2021-02-25  289  	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
> e2ae715d66bf4b Kay Sievers    2012-06-15  290  			     record_size - MTDOOPS_HEADER_SIZE, NULL);
> df92cad8a03e83 John Ogness    2021-02-25  291  	clear_bit(0, &cxt->oops_buf_busy);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  292  
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  293  	if (reason != KMSG_DUMP_OOPS) {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  294  		/* Panics must be written immediately */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  295  		mtdoops_write(cxt, 1);
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  296  	} else {
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  297  		/* For other cases, schedule work to write it "nicely" */
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  298  		schedule_work(&cxt->work_write);
> 2e386e4bac9055 Simon Kagstrom 2009-11-03  299  	}
> c1cf1d57d14922 Mark Tomlinson 2020-09-03  300  }
> 4b23aff083649e Richard Purdie 2007-05-29  301  
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[Petr Mladek]

On Thu 2021-02-25 21:24:25, John Ogness wrote:
> The kmsg_dumper can be called from any context and CPU, possibly
> from multiple CPUs simultaneously. Since the writing of the buffer
> can occur from a later scheduled work queue, the oops buffer must
> be protected against simultaneous dumping.
> 
> Use an atomic bit to mark when the buffer is protected. Release the
> protection in between setting the buffer and the actual writing in
> order for a possible panic (immediate write) to be written during
> the scheduling of a previous oops (delayed write).

Just to be sure. You did not use spin lock to prevent problems
with eventual double unlock in panic(). Do I get it correctly,
please?

> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Anyway, it looks good to me.

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[Petr Mladek]

On Thu 2021-02-25 21:24:25, John Ogness wrote:
> The kmsg_dumper can be called from any context and CPU, possibly
> from multiple CPUs simultaneously. Since the writing of the buffer
> can occur from a later scheduled work queue, the oops buffer must
> be protected against simultaneous dumping.
> 
> Use an atomic bit to mark when the buffer is protected. Release the
> protection in between setting the buffer and the actual writing in
> order for a possible panic (immediate write) to be written during
> the scheduling of a previous oops (delayed write).

Just to be sure. You did not use spin lock to prevent problems
with eventual double unlock in panic(). Do I get it correctly,
please?

> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Anyway, it looks good to me.

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

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Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Thu 2021-02-25 21:24:24, John Ogness wrote:
> The kmsg_dumper can be called from any context and CPU, possibly
> from multiple CPUs simultaneously. Since a static buffer is used
> to retrieve the kernel logs, this buffer must be protected against
> simultaneous dumping. Skip dumping if another context is already
> dumping.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
>  arch/um/kernel/kmsg_dump.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 6516ef1f8274..4869e2cc787c 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/kmsg_dump.h>
> +#include <linux/spinlock.h>
>  #include <linux/console.h>
>  #include <linux/string.h>
>  #include <shared/init.h>
> @@ -9,6 +10,7 @@
>  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  				enum kmsg_dump_reason reason)
>  {
> +	static DEFINE_SPINLOCK(lock);
>  	static char line[1024];
>  	struct console *con;
>  	size_t len = 0;
> @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  	if (con)
>  		return;
>  
> +	if (!spin_trylock(&lock))

I have almost missed this. It is wrong. The last version correctly
used

	if (!spin_trylock_irqsave(&lock, flags))

kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
disabled. We have to store the flags here.

Best Regards,
Petr

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Thu 2021-02-25 21:24:24, John Ogness wrote:
> The kmsg_dumper can be called from any context and CPU, possibly
> from multiple CPUs simultaneously. Since a static buffer is used
> to retrieve the kernel logs, this buffer must be protected against
> simultaneous dumping. Skip dumping if another context is already
> dumping.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
>  arch/um/kernel/kmsg_dump.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> index 6516ef1f8274..4869e2cc787c 100644
> --- a/arch/um/kernel/kmsg_dump.c
> +++ b/arch/um/kernel/kmsg_dump.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/kmsg_dump.h>
> +#include <linux/spinlock.h>
>  #include <linux/console.h>
>  #include <linux/string.h>
>  #include <shared/init.h>
> @@ -9,6 +10,7 @@
>  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  				enum kmsg_dump_reason reason)
>  {
> +	static DEFINE_SPINLOCK(lock);
>  	static char line[1024];
>  	struct console *con;
>  	size_t len = 0;
> @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>  	if (con)
>  		return;
>  
> +	if (!spin_trylock(&lock))

I have almost missed this. It is wrong. The last version correctly
used

	if (!spin_trylock_irqsave(&lock, flags))

kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
disabled. We have to store the flags here.

Best Regards,
Petr

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Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Mon 2021-03-01 17:16:35, Petr Mladek wrote:
> On Thu 2021-02-25 21:24:24, John Ogness wrote:
> > The kmsg_dumper can be called from any context and CPU, possibly
> > from multiple CPUs simultaneously. Since a static buffer is used
> > to retrieve the kernel logs, this buffer must be protected against
> > simultaneous dumping. Skip dumping if another context is already
> > dumping.
> > 
> > Signed-off-by: John Ogness <john.ogness@linutronix.de>
> > Reviewed-by: Petr Mladek <pmladek@suse.com>
> > ---
> >  arch/um/kernel/kmsg_dump.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> > index 6516ef1f8274..4869e2cc787c 100644
> > --- a/arch/um/kernel/kmsg_dump.c
> > +++ b/arch/um/kernel/kmsg_dump.c
> > @@ -1,5 +1,6 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  #include <linux/kmsg_dump.h>
> > +#include <linux/spinlock.h>
> >  #include <linux/console.h>
> >  #include <linux/string.h>
> >  #include <shared/init.h>
> > @@ -9,6 +10,7 @@
> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >  				enum kmsg_dump_reason reason)
> >  {
> > +	static DEFINE_SPINLOCK(lock);
> >  	static char line[1024];
> >  	struct console *con;
> >  	size_t len = 0;
> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >  	if (con)
> >  		return;
> >  
> > +	if (!spin_trylock(&lock))
> 
> I have almost missed this. It is wrong. The last version correctly
> used
> 
> 	if (!spin_trylock_irqsave(&lock, flags))
> 
> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
> disabled. We have to store the flags here.

Ah, I get always confused with these things. spin_trylock() can
actually get called in a context with IRQ disabled. So it is not
as wrong as I thought.

But still. panic() and kmsg_dump() can be called in IRQ context.
So, this function might be called in IRQ context. So, it feels
more correct to use the _irqsafe variant here.

I know that there is the trylock so it probably does not matter much.
Well, the disabled irq might help to serialize the two calls when
one is in normal context and the other would happen in IRQ one.

As I said, using _irqsafe variant looks better to me.

What do you think, please?

Best Regards,
Petr

PS: Heh, IMHO, I do not use an authoritative style too often. But my
feeling is that every time I use it then I am proven to be wrong.
And it has happened again.

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Mon 2021-03-01 17:16:35, Petr Mladek wrote:
> On Thu 2021-02-25 21:24:24, John Ogness wrote:
> > The kmsg_dumper can be called from any context and CPU, possibly
> > from multiple CPUs simultaneously. Since a static buffer is used
> > to retrieve the kernel logs, this buffer must be protected against
> > simultaneous dumping. Skip dumping if another context is already
> > dumping.
> > 
> > Signed-off-by: John Ogness <john.ogness@linutronix.de>
> > Reviewed-by: Petr Mladek <pmladek@suse.com>
> > ---
> >  arch/um/kernel/kmsg_dump.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> > index 6516ef1f8274..4869e2cc787c 100644
> > --- a/arch/um/kernel/kmsg_dump.c
> > +++ b/arch/um/kernel/kmsg_dump.c
> > @@ -1,5 +1,6 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  #include <linux/kmsg_dump.h>
> > +#include <linux/spinlock.h>
> >  #include <linux/console.h>
> >  #include <linux/string.h>
> >  #include <shared/init.h>
> > @@ -9,6 +10,7 @@
> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >  				enum kmsg_dump_reason reason)
> >  {
> > +	static DEFINE_SPINLOCK(lock);
> >  	static char line[1024];
> >  	struct console *con;
> >  	size_t len = 0;
> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >  	if (con)
> >  		return;
> >  
> > +	if (!spin_trylock(&lock))
> 
> I have almost missed this. It is wrong. The last version correctly
> used
> 
> 	if (!spin_trylock_irqsave(&lock, flags))
> 
> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
> disabled. We have to store the flags here.

Ah, I get always confused with these things. spin_trylock() can
actually get called in a context with IRQ disabled. So it is not
as wrong as I thought.

But still. panic() and kmsg_dump() can be called in IRQ context.
So, this function might be called in IRQ context. So, it feels
more correct to use the _irqsafe variant here.

I know that there is the trylock so it probably does not matter much.
Well, the disabled irq might help to serialize the two calls when
one is in normal context and the other would happen in IRQ one.

As I said, using _irqsafe variant looks better to me.

What do you think, please?

Best Regards,
Petr

PS: Heh, IMHO, I do not use an authoritative style too often. But my
feeling is that every time I use it then I am proven to be wrong.
And it has happened again.

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Re: [PATCH next v3 10/15] printk: add syslog_lock

[Petr Mladek]

On Thu 2021-02-25 21:24:33, John Ogness wrote:
> The global variables @syslog_seq, @syslog_partial, @syslog_time
> and write access to @clear_seq are protected by @logbuf_lock.
> Once @logbuf_lock is removed, these variables will need their
> own synchronization method. Introduce @syslog_lock for this
> purpose.
> 
> @syslog_lock is a raw_spin_lock for now. This simplifies the
> transition to removing @logbuf_lock. Once @logbuf_lock and the
> safe buffers are removed, @syslog_lock can change to spin_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH next v3 11/15] printk: kmsg_dumper: remove @active field

[Petr Mladek]

On Thu 2021-02-25 21:24:34, John Ogness wrote:
> All 6 kmsg_dumpers do not benefit from the @active flag:
> 
>   (provide their own synchronization)
>   - arch/powerpc/kernel/nvram_64.c
>   - arch/um/kernel/kmsg_dump.c
>   - drivers/mtd/mtdoops.c
>   - fs/pstore/platform.c
> 
>   (only dump on KMSG_DUMP_PANIC, which does not require
>   synchronization)
>   - arch/powerpc/platforms/powernv/opal-kmsg.c
>   - drivers/hv/vmbus_drv.c
> 
> The other 2 kmsg_dump users also do not rely on @active:
> 
>   (hard-code @active to always be true)
>   - arch/powerpc/xmon/xmon.c
>   - kernel/debug/kdb/kdb_main.c

Great summary!

> Therefore, @active can be removed.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH next v3 11/15] printk: kmsg_dumper: remove @active field

[Petr Mladek]

On Thu 2021-02-25 21:24:34, John Ogness wrote:
> All 6 kmsg_dumpers do not benefit from the @active flag:
> 
>   (provide their own synchronization)
>   - arch/powerpc/kernel/nvram_64.c
>   - arch/um/kernel/kmsg_dump.c
>   - drivers/mtd/mtdoops.c
>   - fs/pstore/platform.c
> 
>   (only dump on KMSG_DUMP_PANIC, which does not require
>   synchronization)
>   - arch/powerpc/platforms/powernv/opal-kmsg.c
>   - drivers/hv/vmbus_drv.c
> 
> The other 2 kmsg_dump users also do not rely on @active:
> 
>   (hard-code @active to always be true)
>   - arch/powerpc/xmon/xmon.c
>   - kernel/debug/kdb/kdb_main.c

Great summary!

> Therefore, @active can be removed.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Thu 2021-02-25 21:24:35, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--
>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);

It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
in all callers.

A solution might be to create the following in include/linux/kmsg_dump.h

#define KMSG_DUMP_ITER_INIT(iter) {	\
	.cur_seq = 0,			\
	.next_seq = U64_MAX,		\
	}

#define DEFINE_KMSG_DUMP_ITER(iter)	\
	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

Then we could do the following at the beginning of both
kmsg_dump_get_buffer() and kmsg_dump_get_line():

	u64 clear_seq = latched_seq_read_nolock(&clear_seq);

	if (iter->cur_seq < clear_seq)
		cur_seq = clear_seq;


I am not completely sure about next_seq:

   + kmsg_dump_get_buffer() will set it for the next call anyway.
     It reads the blocks of messages from the newest.

   + kmsg_dump_get_line() wants to read the entire buffer anyway.
     But there is a small risk of an infinite loop when new messages
     are printed when dumping each line.

It might be better to avoid the infinite loop. We could do the following:

static void check_and_set_iter(struct kmsg_dump_iter)
{
	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
		kmsg_dump_rewind(iter);
}

and call this at the beginning of both kmsg_dump_get_buffer()
and kmsg_dump_get_line()

What do you think?

Note that I do not resist on it. But it might make the API easier to
use from my POV.

Otherwise the patch looks good to me.

Best Regards,
Petr

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Thu 2021-02-25 21:24:35, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--
>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);

It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
in all callers.

A solution might be to create the following in include/linux/kmsg_dump.h

#define KMSG_DUMP_ITER_INIT(iter) {	\
	.cur_seq = 0,			\
	.next_seq = U64_MAX,		\
	}

#define DEFINE_KMSG_DUMP_ITER(iter)	\
	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

Then we could do the following at the beginning of both
kmsg_dump_get_buffer() and kmsg_dump_get_line():

	u64 clear_seq = latched_seq_read_nolock(&clear_seq);

	if (iter->cur_seq < clear_seq)
		cur_seq = clear_seq;


I am not completely sure about next_seq:

   + kmsg_dump_get_buffer() will set it for the next call anyway.
     It reads the blocks of messages from the newest.

   + kmsg_dump_get_line() wants to read the entire buffer anyway.
     But there is a small risk of an infinite loop when new messages
     are printed when dumping each line.

It might be better to avoid the infinite loop. We could do the following:

static void check_and_set_iter(struct kmsg_dump_iter)
{
	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
		kmsg_dump_rewind(iter);
}

and call this at the beginning of both kmsg_dump_get_buffer()
and kmsg_dump_get_line()

What do you think?

Note that I do not resist on it. But it might make the API easier to
use from my POV.

Otherwise the patch looks good to me.

Best Regards,
Petr

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Thu 2021-02-25 21:24:35, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--
>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);

It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
in all callers.

A solution might be to create the following in include/linux/kmsg_dump.h

#define KMSG_DUMP_ITER_INIT(iter) {	\
	.cur_seq = 0,			\
	.next_seq = U64_MAX,		\
	}

#define DEFINE_KMSG_DUMP_ITER(iter)	\
	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

Then we could do the following at the beginning of both
kmsg_dump_get_buffer() and kmsg_dump_get_line():

	u64 clear_seq = latched_seq_read_nolock(&clear_seq);

	if (iter->cur_seq < clear_seq)
		cur_seq = clear_seq;


I am not completely sure about next_seq:

   + kmsg_dump_get_buffer() will set it for the next call anyway.
     It reads the blocks of messages from the newest.

   + kmsg_dump_get_line() wants to read the entire buffer anyway.
     But there is a small risk of an infinite loop when new messages
     are printed when dumping each line.

It might be better to avoid the infinite loop. We could do the following:

static void check_and_set_iter(struct kmsg_dump_iter)
{
	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
		kmsg_dump_rewind(iter);
}

and call this at the beginning of both kmsg_dump_get_buffer()
and kmsg_dump_get_line()

What do you think?

Note that I do not resist on it. But it might make the API easier to
use from my POV.

Otherwise the patch looks good to me.

Best Regards,
Petr

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Thu 2021-02-25 21:24:35, John Ogness wrote:
> Rather than storing the iterator information in the registered
> kmsg_dumper structure, create a separate iterator structure. The
> kmsg_dump_iter structure can reside on the stack of the caller, thus
> allowing lockless use of the kmsg_dump functions.
> 
> This change also means that the kmsg_dumper dump() callback no
> longer needs to pass in the kmsg_dumper as an argument. If
> kmsg_dumpers want to access the kernel logs, they can use the new
> iterator.
> 
> Update the kmsg_dumper callback prototype. Update code that accesses
> the kernel logs using the kmsg_dumper structure to use the new
> kmsg_dump_iter structure. For kmsg_dumpers, this also means adding a
> call to kmsg_dump_rewind() to initialize the iterator.
> 
> All this is in preparation for removal of @logbuf_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
>  arch/powerpc/kernel/nvram_64.c             | 14 +++---
>  arch/powerpc/platforms/powernv/opal-kmsg.c |  3 +-
>  arch/powerpc/xmon/xmon.c                   |  6 +--
>  arch/um/kernel/kmsg_dump.c                 |  8 +--
>  drivers/hv/vmbus_drv.c                     |  7 +--
>  drivers/mtd/mtdoops.c                      |  8 +--
>  fs/pstore/platform.c                       |  8 +--
>  include/linux/kmsg_dump.h                  | 38 ++++++++-------
>  kernel/debug/kdb/kdb_main.c                | 10 ++--
>  kernel/printk/printk.c                     | 57 ++++++++++------------
>  10 files changed, 81 insertions(+), 78 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> index 532f22637783..5a64b24a91c2 100644
> --- a/arch/powerpc/kernel/nvram_64.c
> +++ b/arch/powerpc/kernel/nvram_64.c
> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>  	NULL
>  };
>  
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason);
> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>  
>  static struct kmsg_dumper nvram_kmsg_dumper = {
>  	.dump = oops_to_nvram
> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>   * that we think will compress sufficiently to fit in the lnx,oops-log
>   * partition.  If that's too much, go back and capture uncompressed text.
>   */
> -static void oops_to_nvram(struct kmsg_dumper *dumper,
> -			  enum kmsg_dump_reason reason)
> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>  {
>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>  	static unsigned int oops_count = 0;
> +	static struct kmsg_dump_iter iter;
>  	static bool panicking = false;
>  	static DEFINE_SPINLOCK(lock);
>  	unsigned long flags;
> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>  		return;
>  
>  	if (big_oops_buf) {
> -		kmsg_dump_get_buffer(dumper, false,
> +		kmsg_dump_rewind(&iter);

It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
in all callers.

A solution might be to create the following in include/linux/kmsg_dump.h

#define KMSG_DUMP_ITER_INIT(iter) {	\
	.cur_seq = 0,			\
	.next_seq = U64_MAX,		\
	}

#define DEFINE_KMSG_DUMP_ITER(iter)	\
	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

Then we could do the following at the beginning of both
kmsg_dump_get_buffer() and kmsg_dump_get_line():

	u64 clear_seq = latched_seq_read_nolock(&clear_seq);

	if (iter->cur_seq < clear_seq)
		cur_seq = clear_seq;


I am not completely sure about next_seq:

   + kmsg_dump_get_buffer() will set it for the next call anyway.
     It reads the blocks of messages from the newest.

   + kmsg_dump_get_line() wants to read the entire buffer anyway.
     But there is a small risk of an infinite loop when new messages
     are printed when dumping each line.

It might be better to avoid the infinite loop. We could do the following:

static void check_and_set_iter(struct kmsg_dump_iter)
{
	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
		kmsg_dump_rewind(iter);
}

and call this at the beginning of both kmsg_dump_get_buffer()
and kmsg_dump_get_line()

What do you think?

Note that I do not resist on it. But it might make the API easier to
use from my POV.

Otherwise the patch looks good to me.

Best Regards,
Petr

_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
>> > index 6516ef1f8274..4869e2cc787c 100644
>> > --- a/arch/um/kernel/kmsg_dump.c
>> > +++ b/arch/um/kernel/kmsg_dump.c
>> > @@ -1,5 +1,6 @@
>> >  // SPDX-License-Identifier: GPL-2.0
>> >  #include <linux/kmsg_dump.h>
>> > +#include <linux/spinlock.h>
>> >  #include <linux/console.h>
>> >  #include <linux/string.h>
>> >  #include <shared/init.h>
>> > @@ -9,6 +10,7 @@
>> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>> >  				enum kmsg_dump_reason reason)
>> >  {
>> > +	static DEFINE_SPINLOCK(lock);
>> >  	static char line[1024];
>> >  	struct console *con;
>> >  	size_t len = 0;
>> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>> >  	if (con)
>> >  		return;
>> >  
>> > +	if (!spin_trylock(&lock))
>> 
>> I have almost missed this. It is wrong. The last version correctly
>> used
>> 
>> 	if (!spin_trylock_irqsave(&lock, flags))
>> 
>> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
>> disabled. We have to store the flags here.
>
> Ah, I get always confused with these things. spin_trylock() can
> actually get called in a context with IRQ disabled. So it is not
> as wrong as I thought.
>
> But still. panic() and kmsg_dump() can be called in IRQ context.
> So, this function might be called in IRQ context. So, it feels
> more correct to use the _irqsafe variant here.
>
> I know that there is the trylock so it probably does not matter much.
> Well, the disabled irq might help to serialize the two calls when
> one is in normal context and the other would happen in IRQ one.
>
> As I said, using _irqsafe variant looks better to me.

For the record, the reason I removed the _irqsave for v3 is because I
felt like it was misleading, appearing to be necessary when it is not.

I think anyone could argue both sides. But it really doesn't matter
(especially for arch/um). I will use the _irqsave variant for v4. I am
OK with that.

John Ogness

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
>> > index 6516ef1f8274..4869e2cc787c 100644
>> > --- a/arch/um/kernel/kmsg_dump.c
>> > +++ b/arch/um/kernel/kmsg_dump.c
>> > @@ -1,5 +1,6 @@
>> >  // SPDX-License-Identifier: GPL-2.0
>> >  #include <linux/kmsg_dump.h>
>> > +#include <linux/spinlock.h>
>> >  #include <linux/console.h>
>> >  #include <linux/string.h>
>> >  #include <shared/init.h>
>> > @@ -9,6 +10,7 @@
>> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>> >  				enum kmsg_dump_reason reason)
>> >  {
>> > +	static DEFINE_SPINLOCK(lock);
>> >  	static char line[1024];
>> >  	struct console *con;
>> >  	size_t len = 0;
>> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
>> >  	if (con)
>> >  		return;
>> >  
>> > +	if (!spin_trylock(&lock))
>> 
>> I have almost missed this. It is wrong. The last version correctly
>> used
>> 
>> 	if (!spin_trylock_irqsave(&lock, flags))
>> 
>> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
>> disabled. We have to store the flags here.
>
> Ah, I get always confused with these things. spin_trylock() can
> actually get called in a context with IRQ disabled. So it is not
> as wrong as I thought.
>
> But still. panic() and kmsg_dump() can be called in IRQ context.
> So, this function might be called in IRQ context. So, it feels
> more correct to use the _irqsafe variant here.
>
> I know that there is the trylock so it probably does not matter much.
> Well, the disabled irq might help to serialize the two calls when
> one is in normal context and the other would happen in IRQ one.
>
> As I said, using _irqsafe variant looks better to me.

For the record, the reason I removed the _irqsave for v3 is because I
felt like it was misleading, appearing to be necessary when it is not.

I think anyone could argue both sides. But it really doesn't matter
(especially for arch/um). I will use the _irqsave variant for v4. I am
OK with that.

John Ogness

_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Tue 2021-03-02 09:06:07, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> >> > index 6516ef1f8274..4869e2cc787c 100644
> >> > --- a/arch/um/kernel/kmsg_dump.c
> >> > +++ b/arch/um/kernel/kmsg_dump.c
> >> > @@ -1,5 +1,6 @@
> >> >  // SPDX-License-Identifier: GPL-2.0
> >> >  #include <linux/kmsg_dump.h>
> >> > +#include <linux/spinlock.h>
> >> >  #include <linux/console.h>
> >> >  #include <linux/string.h>
> >> >  #include <shared/init.h>
> >> > @@ -9,6 +10,7 @@
> >> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >> >  				enum kmsg_dump_reason reason)
> >> >  {
> >> > +	static DEFINE_SPINLOCK(lock);
> >> >  	static char line[1024];
> >> >  	struct console *con;
> >> >  	size_t len = 0;
> >> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >> >  	if (con)
> >> >  		return;
> >> >  
> >> > +	if (!spin_trylock(&lock))
> >> 
> >> I have almost missed this. It is wrong. The last version correctly
> >> used
> >> 
> >> 	if (!spin_trylock_irqsave(&lock, flags))
> >> 
> >> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
> >> disabled. We have to store the flags here.
> >
> > Ah, I get always confused with these things. spin_trylock() can
> > actually get called in a context with IRQ disabled. So it is not
> > as wrong as I thought.
> >
> > But still. panic() and kmsg_dump() can be called in IRQ context.
> > So, this function might be called in IRQ context. So, it feels
> > more correct to use the _irqsafe variant here.
> >
> > I know that there is the trylock so it probably does not matter much.
> > Well, the disabled irq might help to serialize the two calls when
> > one is in normal context and the other would happen in IRQ one.
> >
> > As I said, using _irqsafe variant looks better to me.
> 
> For the record, the reason I removed the _irqsave for v3 is because I
> felt like it was misleading, appearing to be necessary when it is not.
> 
> I think anyone could argue both sides.

Yeah, I could imagine myself to have different opinion another day
or year. I am sorry for the noise.

> But it really doesn't matter
> (especially for arch/um). I will use the _irqsave variant for v4. I am
> OK with that.

Please do, if it is easy. You are going to send v4 anyway.

Best Regards,
Petr

Re: [PATCH next v3 01/15] um: synchronize kmsg_dumper

[Petr Mladek]

On Tue 2021-03-02 09:06:07, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> > diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
> >> > index 6516ef1f8274..4869e2cc787c 100644
> >> > --- a/arch/um/kernel/kmsg_dump.c
> >> > +++ b/arch/um/kernel/kmsg_dump.c
> >> > @@ -1,5 +1,6 @@
> >> >  // SPDX-License-Identifier: GPL-2.0
> >> >  #include <linux/kmsg_dump.h>
> >> > +#include <linux/spinlock.h>
> >> >  #include <linux/console.h>
> >> >  #include <linux/string.h>
> >> >  #include <shared/init.h>
> >> > @@ -9,6 +10,7 @@
> >> >  static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >> >  				enum kmsg_dump_reason reason)
> >> >  {
> >> > +	static DEFINE_SPINLOCK(lock);
> >> >  	static char line[1024];
> >> >  	struct console *con;
> >> >  	size_t len = 0;
> >> > @@ -29,11 +31,16 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
> >> >  	if (con)
> >> >  		return;
> >> >  
> >> > +	if (!spin_trylock(&lock))
> >> 
> >> I have almost missed this. It is wrong. The last version correctly
> >> used
> >> 
> >> 	if (!spin_trylock_irqsave(&lock, flags))
> >> 
> >> kmsg_dump(KMSG_DUMP_PANIC) is called in panic() with interrupts
> >> disabled. We have to store the flags here.
> >
> > Ah, I get always confused with these things. spin_trylock() can
> > actually get called in a context with IRQ disabled. So it is not
> > as wrong as I thought.
> >
> > But still. panic() and kmsg_dump() can be called in IRQ context.
> > So, this function might be called in IRQ context. So, it feels
> > more correct to use the _irqsafe variant here.
> >
> > I know that there is the trylock so it probably does not matter much.
> > Well, the disabled irq might help to serialize the two calls when
> > one is in normal context and the other would happen in IRQ one.
> >
> > As I said, using _irqsafe variant looks better to me.
> 
> For the record, the reason I removed the _irqsave for v3 is because I
> felt like it was misleading, appearing to be necessary when it is not.
> 
> I think anyone could argue both sides.

Yeah, I could imagine myself to have different opinion another day
or year. I am sorry for the noise.

> But it really doesn't matter
> (especially for arch/um). I will use the _irqsave variant for v4. I am
> OK with that.

Please do, if it is easy. You are going to send v4 anyway.

Best Regards,
Petr

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Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> The kmsg_dumper can be called from any context and CPU, possibly
>> from multiple CPUs simultaneously. Since the writing of the buffer
>> can occur from a later scheduled work queue, the oops buffer must
>> be protected against simultaneous dumping.
>> 
>> Use an atomic bit to mark when the buffer is protected. Release the
>> protection in between setting the buffer and the actual writing in
>> order for a possible panic (immediate write) to be written during
>> the scheduling of a previous oops (delayed write).
>
> Just to be sure. You did not use spin lock to prevent problems
> with eventual double unlock in panic(). Do I get it correctly,
> please?

I do not understand what possible double unlock you are referring to.

I chose not to use spinlocks because I wanted something that does not
cause any scheduling or preemption side-effects for mtd. The mtd dumper
sometimes dumps directly, sometimes delayed (via scheduled work), and
they use different mtd callbacks in different contexts.

mtd_write() expects to be called in a non-atomic context. The callbacks
can take a mutex.

John Ogness

Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> The kmsg_dumper can be called from any context and CPU, possibly
>> from multiple CPUs simultaneously. Since the writing of the buffer
>> can occur from a later scheduled work queue, the oops buffer must
>> be protected against simultaneous dumping.
>> 
>> Use an atomic bit to mark when the buffer is protected. Release the
>> protection in between setting the buffer and the actual writing in
>> order for a possible panic (immediate write) to be written during
>> the scheduling of a previous oops (delayed write).
>
> Just to be sure. You did not use spin lock to prevent problems
> with eventual double unlock in panic(). Do I get it correctly,
> please?

I do not understand what possible double unlock you are referring to.

I chose not to use spinlocks because I wanted something that does not
cause any scheduling or preemption side-effects for mtd. The mtd dumper
sometimes dumps directly, sometimes delayed (via scheduled work), and
they use different mtd callbacks in different contexts.

mtd_write() expects to be called in a non-atomic context. The callbacks
can take a mutex.

John Ogness

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 13/15] printk: remove logbuf_lock

[Petr Mladek]

On Thu 2021-02-25 21:24:36, John Ogness wrote:
> Since the ringbuffer is lockless, there is no need for it to be
> protected by @logbuf_lock. Remove @logbuf_lock.
> 
> @console_seq, @exclusive_console_stop_seq, @console_dropped are
> protected by @console_lock.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr

Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[Petr Mladek]

On Tue 2021-03-02 11:45:27, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> The kmsg_dumper can be called from any context and CPU, possibly
> >> from multiple CPUs simultaneously. Since the writing of the buffer
> >> can occur from a later scheduled work queue, the oops buffer must
> >> be protected against simultaneous dumping.
> >> 
> >> Use an atomic bit to mark when the buffer is protected. Release the
> >> protection in between setting the buffer and the actual writing in
> >> order for a possible panic (immediate write) to be written during
> >> the scheduling of a previous oops (delayed write).
> >
> > Just to be sure. You did not use spin lock to prevent problems
> > with eventual double unlock in panic(). Do I get it correctly,
> > please?
> 
> I do not understand what possible double unlock you are referring to.

I was wrong. I meant the tricks that are under in console drivrers,
for example:

static void mvebu_uart_console_write(struct console *co, const char *s,
				     unsigned int count)
{
	int locked = 1;

	if (oops_in_progress)
		locked = spin_trylock_irqsave(&port->lock, flags);
	else
		spin_lock_irqsave(&port->lock, flags);

	/* do the job */

	if (locked)
		spin_unlock_irqrestore(&port->lock, flags);
}

But this is not a problem here because the kmsg dumper bails out
when the lock could not be taken.

> I chose not to use spinlocks because I wanted something that does not
> cause any scheduling or preemption side-effects for mtd. The mtd dumper
> sometimes dumps directly, sometimes delayed (via scheduled work), and
> they use different mtd callbacks in different contexts.
>
> mtd_write() expects to be called in a non-atomic context. The callbacks
> can take a mutex.

Makes sense. Could you please mention this in the commit message?

Best Regards,
Petr

Re: [PATCH next v3 02/15] mtd: mtdoops: synchronize kmsg_dumper

[Petr Mladek]

On Tue 2021-03-02 11:45:27, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> The kmsg_dumper can be called from any context and CPU, possibly
> >> from multiple CPUs simultaneously. Since the writing of the buffer
> >> can occur from a later scheduled work queue, the oops buffer must
> >> be protected against simultaneous dumping.
> >> 
> >> Use an atomic bit to mark when the buffer is protected. Release the
> >> protection in between setting the buffer and the actual writing in
> >> order for a possible panic (immediate write) to be written during
> >> the scheduling of a previous oops (delayed write).
> >
> > Just to be sure. You did not use spin lock to prevent problems
> > with eventual double unlock in panic(). Do I get it correctly,
> > please?
> 
> I do not understand what possible double unlock you are referring to.

I was wrong. I meant the tricks that are under in console drivrers,
for example:

static void mvebu_uart_console_write(struct console *co, const char *s,
				     unsigned int count)
{
	int locked = 1;

	if (oops_in_progress)
		locked = spin_trylock_irqsave(&port->lock, flags);
	else
		spin_lock_irqsave(&port->lock, flags);

	/* do the job */

	if (locked)
		spin_unlock_irqrestore(&port->lock, flags);
}

But this is not a problem here because the kmsg dumper bails out
when the lock could not be taken.

> I chose not to use spinlocks because I wanted something that does not
> cause any scheduling or preemption side-effects for mtd. The mtd dumper
> sometimes dumps directly, sometimes delayed (via scheduled work), and
> they use different mtd callbacks in different contexts.
>
> mtd_write() expects to be called in a non-atomic context. The callbacks
> can take a mutex.

Makes sense. Could you please mention this in the commit message?

Best Regards,
Petr

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
>> index 532f22637783..5a64b24a91c2 100644
>> --- a/arch/powerpc/kernel/nvram_64.c
>> +++ b/arch/powerpc/kernel/nvram_64.c
>> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>>  	NULL
>>  };
>>  
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason);
>> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>>  
>>  static struct kmsg_dumper nvram_kmsg_dumper = {
>>  	.dump = oops_to_nvram
>> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>>   * that we think will compress sufficiently to fit in the lnx,oops-log
>>   * partition.  If that's too much, go back and capture uncompressed text.
>>   */
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason)
>> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>>  {
>>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>>  	static unsigned int oops_count = 0;
>> +	static struct kmsg_dump_iter iter;
>>  	static bool panicking = false;
>>  	static DEFINE_SPINLOCK(lock);
>>  	unsigned long flags;
>> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>>  		return;
>>  
>>  	if (big_oops_buf) {
>> -		kmsg_dump_get_buffer(dumper, false,
>> +		kmsg_dump_rewind(&iter);
>
> It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> in all callers.
>
> A solution might be to create the following in include/linux/kmsg_dump.h
>
> #define KMSG_DUMP_ITER_INIT(iter) {	\
> 	.cur_seq = 0,			\
> 	.next_seq = U64_MAX,		\
> 	}
>
> #define DEFINE_KMSG_DUMP_ITER(iter)	\
> 	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

For this caller (arch/powerpc/kernel/nvram_64.c) and for
(kernel/debug/kdb/kdb_main.c), kmsg_dump_rewind() is called twice within
the dumper. So rewind will still be used there.

> Then we could do the following at the beginning of both
> kmsg_dump_get_buffer() and kmsg_dump_get_line():
>
> 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
>
> 	if (iter->cur_seq < clear_seq)
> 		cur_seq = clear_seq;

I suppose we need to add this part anyway, if we want to enforce that
records before @clear_seq are not to be available for dumpers.

> I am not completely sure about next_seq:
>
>    + kmsg_dump_get_buffer() will set it for the next call anyway.
>      It reads the blocks of messages from the newest.
>
>    + kmsg_dump_get_line() wants to read the entire buffer anyway.
>      But there is a small risk of an infinite loop when new messages
>      are printed when dumping each line.
>
> It might be better to avoid the infinite loop. We could do the following:
>
> static void check_and_set_iter(struct kmsg_dump_iter)
> {
> 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> 		kmsg_dump_rewind(iter);
> }
>
> and call this at the beginning of both kmsg_dump_get_buffer()
> and kmsg_dump_get_line()
>
> What do you think?

On a technical level, it does not make any difference. It is pure
cosmetic.

Personally, I prefer the rewind directly before the kmsg_dump_get calls
because it puts the initializer directly next to the user.

As an example to illustrate my view, I prefer:

    for (i = 0; i < n; i++)
        ...;

instead of:

    int i = 0;

    ...

    for (; i < n; i++)
        ...;

Also, I do not really like the special use of 0/U64_MAX to identify
special actions of the kmsg_dump_get functions.

> Note that I do not resist on it. But it might make the API easier to
> use from my POV.

Since you do not resist, I will keep the API the same for v4. But I will
add the @clear_seq check to the kmsg_dump_get functions.

John Ogness

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
>> index 532f22637783..5a64b24a91c2 100644
>> --- a/arch/powerpc/kernel/nvram_64.c
>> +++ b/arch/powerpc/kernel/nvram_64.c
>> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>>  	NULL
>>  };
>>  
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason);
>> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>>  
>>  static struct kmsg_dumper nvram_kmsg_dumper = {
>>  	.dump = oops_to_nvram
>> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>>   * that we think will compress sufficiently to fit in the lnx,oops-log
>>   * partition.  If that's too much, go back and capture uncompressed text.
>>   */
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason)
>> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>>  {
>>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>>  	static unsigned int oops_count = 0;
>> +	static struct kmsg_dump_iter iter;
>>  	static bool panicking = false;
>>  	static DEFINE_SPINLOCK(lock);
>>  	unsigned long flags;
>> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>>  		return;
>>  
>>  	if (big_oops_buf) {
>> -		kmsg_dump_get_buffer(dumper, false,
>> +		kmsg_dump_rewind(&iter);
>
> It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> in all callers.
>
> A solution might be to create the following in include/linux/kmsg_dump.h
>
> #define KMSG_DUMP_ITER_INIT(iter) {	\
> 	.cur_seq = 0,			\
> 	.next_seq = U64_MAX,		\
> 	}
>
> #define DEFINE_KMSG_DUMP_ITER(iter)	\
> 	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

For this caller (arch/powerpc/kernel/nvram_64.c) and for
(kernel/debug/kdb/kdb_main.c), kmsg_dump_rewind() is called twice within
the dumper. So rewind will still be used there.

> Then we could do the following at the beginning of both
> kmsg_dump_get_buffer() and kmsg_dump_get_line():
>
> 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
>
> 	if (iter->cur_seq < clear_seq)
> 		cur_seq = clear_seq;

I suppose we need to add this part anyway, if we want to enforce that
records before @clear_seq are not to be available for dumpers.

> I am not completely sure about next_seq:
>
>    + kmsg_dump_get_buffer() will set it for the next call anyway.
>      It reads the blocks of messages from the newest.
>
>    + kmsg_dump_get_line() wants to read the entire buffer anyway.
>      But there is a small risk of an infinite loop when new messages
>      are printed when dumping each line.
>
> It might be better to avoid the infinite loop. We could do the following:
>
> static void check_and_set_iter(struct kmsg_dump_iter)
> {
> 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> 		kmsg_dump_rewind(iter);
> }
>
> and call this at the beginning of both kmsg_dump_get_buffer()
> and kmsg_dump_get_line()
>
> What do you think?

On a technical level, it does not make any difference. It is pure
cosmetic.

Personally, I prefer the rewind directly before the kmsg_dump_get calls
because it puts the initializer directly next to the user.

As an example to illustrate my view, I prefer:

    for (i = 0; i < n; i++)
        ...;

instead of:

    int i = 0;

    ...

    for (; i < n; i++)
        ...;

Also, I do not really like the special use of 0/U64_MAX to identify
special actions of the kmsg_dump_get functions.

> Note that I do not resist on it. But it might make the API easier to
> use from my POV.

Since you do not resist, I will keep the API the same for v4. But I will
add the @clear_seq check to the kmsg_dump_get functions.

John Ogness

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[John Ogness]

On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
>> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
>> index 532f22637783..5a64b24a91c2 100644
>> --- a/arch/powerpc/kernel/nvram_64.c
>> +++ b/arch/powerpc/kernel/nvram_64.c
>> @@ -72,8 +72,7 @@ static const char *nvram_os_partitions[] = {
>>  	NULL
>>  };
>>  
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason);
>> +static void oops_to_nvram(enum kmsg_dump_reason reason);
>>  
>>  static struct kmsg_dumper nvram_kmsg_dumper = {
>>  	.dump = oops_to_nvram
>> @@ -642,11 +641,11 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
>>   * that we think will compress sufficiently to fit in the lnx,oops-log
>>   * partition.  If that's too much, go back and capture uncompressed text.
>>   */
>> -static void oops_to_nvram(struct kmsg_dumper *dumper,
>> -			  enum kmsg_dump_reason reason)
>> +static void oops_to_nvram(enum kmsg_dump_reason reason)
>>  {
>>  	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
>>  	static unsigned int oops_count = 0;
>> +	static struct kmsg_dump_iter iter;
>>  	static bool panicking = false;
>>  	static DEFINE_SPINLOCK(lock);
>>  	unsigned long flags;
>> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
>>  		return;
>>  
>>  	if (big_oops_buf) {
>> -		kmsg_dump_get_buffer(dumper, false,
>> +		kmsg_dump_rewind(&iter);
>
> It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> in all callers.
>
> A solution might be to create the following in include/linux/kmsg_dump.h
>
> #define KMSG_DUMP_ITER_INIT(iter) {	\
> 	.cur_seq = 0,			\
> 	.next_seq = U64_MAX,		\
> 	}
>
> #define DEFINE_KMSG_DUMP_ITER(iter)	\
> 	struct kmsg_dump_iter iter = KMSG_DUMP_ITER_INIT(iter)

For this caller (arch/powerpc/kernel/nvram_64.c) and for
(kernel/debug/kdb/kdb_main.c), kmsg_dump_rewind() is called twice within
the dumper. So rewind will still be used there.

> Then we could do the following at the beginning of both
> kmsg_dump_get_buffer() and kmsg_dump_get_line():
>
> 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
>
> 	if (iter->cur_seq < clear_seq)
> 		cur_seq = clear_seq;

I suppose we need to add this part anyway, if we want to enforce that
records before @clear_seq are not to be available for dumpers.

> I am not completely sure about next_seq:
>
>    + kmsg_dump_get_buffer() will set it for the next call anyway.
>      It reads the blocks of messages from the newest.
>
>    + kmsg_dump_get_line() wants to read the entire buffer anyway.
>      But there is a small risk of an infinite loop when new messages
>      are printed when dumping each line.
>
> It might be better to avoid the infinite loop. We could do the following:
>
> static void check_and_set_iter(struct kmsg_dump_iter)
> {
> 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> 		kmsg_dump_rewind(iter);
> }
>
> and call this at the beginning of both kmsg_dump_get_buffer()
> and kmsg_dump_get_line()
>
> What do you think?

On a technical level, it does not make any difference. It is pure
cosmetic.

Personally, I prefer the rewind directly before the kmsg_dump_get calls
because it puts the initializer directly next to the user.

As an example to illustrate my view, I prefer:

    for (i = 0; i < n; i++)
        ...;

instead of:

    int i = 0;

    ...

    for (; i < n; i++)
        ...;

Also, I do not really like the special use of 0/U64_MAX to identify
special actions of the kmsg_dump_get functions.

> Note that I do not resist on it. But it might make the API easier to
> use from my POV.

Since you do not resist, I will keep the API the same for v4. But I will
add the @clear_seq check to the kmsg_dump_get functions.

John Ogness

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: [PATCH next v3 07/15] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

[Geert Uytterhoeven]

Hi John,

On Thu, Feb 25, 2021 at 9:30 PM John Ogness <john.ogness@linutronix.de> wrote:
> Instead of using "LOG_LINE_MAX + PREFIX_MAX" for temporary buffer
> sizes, introduce CONSOLE_LOG_MAX. This represents the maximum size
> that is allowed to be printed to the console for a single record.
>
> Rather than setting CONSOLE_LOG_MAX to "LOG_LINE_MAX + PREFIX_MAX"
> (1024), increase it to 4096. With a larger buffer size, multi-line
> records that are nearly LOG_LINE_MAX in length will have a better
> chance of being fully printed. (When formatting a record for the
> console, each line of a multi-line record is prepended with a copy
> of the prefix.)
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>

Thanks for your patch!

This increases kernel size by more than 3 KiB, which affects small
devices (e.g. SoCs with 10 MiB of SRAM inside).
Who is printing such long lines to the console?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Tue 2021-03-02 14:20:51, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> >> index 532f22637783..5a64b24a91c2 100644
> >> --- a/arch/powerpc/kernel/nvram_64.c
> >> +++ b/arch/powerpc/kernel/nvram_64.c
> >> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
> >>  		return;
> >>  
> >>  	if (big_oops_buf) {
> >> -		kmsg_dump_get_buffer(dumper, false,
> >> +		kmsg_dump_rewind(&iter);
> >
> > It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> > in all callers.
> >
> > A solution might be to create the following in include/linux/kmsg_dump.h
> >
> > Then we could do the following at the beginning of both
> > kmsg_dump_get_buffer() and kmsg_dump_get_line():
> >
> > 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
> >
> > 	if (iter->cur_seq < clear_seq)
> > 		cur_seq = clear_seq;
> 
> I suppose we need to add this part anyway, if we want to enforce that
> records before @clear_seq are not to be available for dumpers.

Yup.

> > It might be better to avoid the infinite loop. We could do the following:
> >
> > static void check_and_set_iter(struct kmsg_dump_iter)
> > {
> > 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> > 		kmsg_dump_rewind(iter);
> > }
> >
> > and call this at the beginning of both kmsg_dump_get_buffer()
> > and kmsg_dump_get_line()
> >
> > What do you think?
> 
> On a technical level, it does not make any difference. It is pure
> cosmetic.

Yup.

> Personally, I prefer the rewind directly before the kmsg_dump_get calls
> because it puts the initializer directly next to the user.
> 
> As an example to illustrate my view, I prefer:
> 
>     for (i = 0; i < n; i++)
>         ...;
> 
> instead of:
> 
>     int i = 0;
> 
>     ...
> 
>     for (; i < n; i++)
>         ...;
> 
> Also, I do not really like the special use of 0/U64_MAX to identify
> special actions of the kmsg_dump_get functions.

Fair enough.

> > Note that I do not resist on it. But it might make the API easier to
> > use from my POV.
> 
> Since you do not resist, I will keep the API the same for v4. But I will
> add the @clear_seq check to the kmsg_dump_get functions.

Go for it.

Best Regards,
Petr

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Tue 2021-03-02 14:20:51, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> >> index 532f22637783..5a64b24a91c2 100644
> >> --- a/arch/powerpc/kernel/nvram_64.c
> >> +++ b/arch/powerpc/kernel/nvram_64.c
> >> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
> >>  		return;
> >>  
> >>  	if (big_oops_buf) {
> >> -		kmsg_dump_get_buffer(dumper, false,
> >> +		kmsg_dump_rewind(&iter);
> >
> > It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> > in all callers.
> >
> > A solution might be to create the following in include/linux/kmsg_dump.h
> >
> > Then we could do the following at the beginning of both
> > kmsg_dump_get_buffer() and kmsg_dump_get_line():
> >
> > 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
> >
> > 	if (iter->cur_seq < clear_seq)
> > 		cur_seq = clear_seq;
> 
> I suppose we need to add this part anyway, if we want to enforce that
> records before @clear_seq are not to be available for dumpers.

Yup.

> > It might be better to avoid the infinite loop. We could do the following:
> >
> > static void check_and_set_iter(struct kmsg_dump_iter)
> > {
> > 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> > 		kmsg_dump_rewind(iter);
> > }
> >
> > and call this at the beginning of both kmsg_dump_get_buffer()
> > and kmsg_dump_get_line()
> >
> > What do you think?
> 
> On a technical level, it does not make any difference. It is pure
> cosmetic.

Yup.

> Personally, I prefer the rewind directly before the kmsg_dump_get calls
> because it puts the initializer directly next to the user.
> 
> As an example to illustrate my view, I prefer:
> 
>     for (i = 0; i < n; i++)
>         ...;
> 
> instead of:
> 
>     int i = 0;
> 
>     ...
> 
>     for (; i < n; i++)
>         ...;
> 
> Also, I do not really like the special use of 0/U64_MAX to identify
> special actions of the kmsg_dump_get functions.

Fair enough.

> > Note that I do not resist on it. But it might make the API easier to
> > use from my POV.
> 
> Since you do not resist, I will keep the API the same for v4. But I will
> add the @clear_seq check to the kmsg_dump_get functions.

Go for it.

Best Regards,
Petr

Re: [PATCH next v3 12/15] printk: introduce a kmsg_dump iterator

[Petr Mladek]

On Tue 2021-03-02 14:20:51, John Ogness wrote:
> On 2021-03-01, Petr Mladek <pmladek@suse.com> wrote:
> >> diff --git a/arch/powerpc/kernel/nvram_64.c b/arch/powerpc/kernel/nvram_64.c
> >> index 532f22637783..5a64b24a91c2 100644
> >> --- a/arch/powerpc/kernel/nvram_64.c
> >> +++ b/arch/powerpc/kernel/nvram_64.c
> >> @@ -681,13 +680,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
> >>  		return;
> >>  
> >>  	if (big_oops_buf) {
> >> -		kmsg_dump_get_buffer(dumper, false,
> >> +		kmsg_dump_rewind(&iter);
> >
> > It would be nice to get rid of the kmsg_dump_rewind(&iter) calls
> > in all callers.
> >
> > A solution might be to create the following in include/linux/kmsg_dump.h
> >
> > Then we could do the following at the beginning of both
> > kmsg_dump_get_buffer() and kmsg_dump_get_line():
> >
> > 	u64 clear_seq = latched_seq_read_nolock(&clear_seq);
> >
> > 	if (iter->cur_seq < clear_seq)
> > 		cur_seq = clear_seq;
> 
> I suppose we need to add this part anyway, if we want to enforce that
> records before @clear_seq are not to be available for dumpers.

Yup.

> > It might be better to avoid the infinite loop. We could do the following:
> >
> > static void check_and_set_iter(struct kmsg_dump_iter)
> > {
> > 	if (iter->cur_seq == 0 && iter->next_seq == U64_MAX) {
> > 		kmsg_dump_rewind(iter);
> > }
> >
> > and call this at the beginning of both kmsg_dump_get_buffer()
> > and kmsg_dump_get_line()
> >
> > What do you think?
> 
> On a technical level, it does not make any difference. It is pure
> cosmetic.

Yup.

> Personally, I prefer the rewind directly before the kmsg_dump_get calls
> because it puts the initializer directly next to the user.
> 
> As an example to illustrate my view, I prefer:
> 
>     for (i = 0; i < n; i++)
>         ...;
> 
> instead of:
> 
>     int i = 0;
> 
>     ...
> 
>     for (; i < n; i++)
>         ...;
> 
> Also, I do not really like the special use of 0/U64_MAX to identify
> special actions of the kmsg_dump_get functions.

Fair enough.

> > Note that I do not resist on it. But it might make the API easier to
> > use from my POV.
> 
> Since you do not resist, I will keep the API the same for v4. But I will
> add the @clear_seq check to the kmsg_dump_get functions.

Go for it.

Best Regards,
Petr

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Re: [PATCH next v3 07/15] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

[Geert Uytterhoeven]

Hi John,

On Tue, Mar 2, 2021 at 2:54 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Thu, Feb 25, 2021 at 9:30 PM John Ogness <john.ogness@linutronix.de> wrote:
> > Instead of using "LOG_LINE_MAX + PREFIX_MAX" for temporary buffer
> > sizes, introduce CONSOLE_LOG_MAX. This represents the maximum size
> > that is allowed to be printed to the console for a single record.
> >
> > Rather than setting CONSOLE_LOG_MAX to "LOG_LINE_MAX + PREFIX_MAX"
> > (1024), increase it to 4096. With a larger buffer size, multi-line
> > records that are nearly LOG_LINE_MAX in length will have a better
> > chance of being fully printed. (When formatting a record for the
> > console, each line of a multi-line record is prepended with a copy
> > of the prefix.)
> >
> > Signed-off-by: John Ogness <john.ogness@linutronix.de>
> > Reviewed-by: Petr Mladek <pmladek@suse.com>
>
> Thanks for your patch!
>
> This increases kernel size by more than 3 KiB, which affects small
> devices (e.g. SoCs with 10 MiB of SRAM inside).
> Who is printing such long lines to the console?

BTW, printing a single line of 1024 characters to a serial console at
115200 bps takes almost 100 ms.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH next v3 07/15] printk: introduce CONSOLE_LOG_MAX for improved multi-line support

[John Ogness]

Hi Geert,

On 2021-03-02, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Tue, Mar 2, 2021 at 2:54 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>> On Thu, Feb 25, 2021 at 9:30 PM John Ogness <john.ogness@linutronix.de> wrote:
>>> Instead of using "LOG_LINE_MAX + PREFIX_MAX" for temporary buffer
>>> sizes, introduce CONSOLE_LOG_MAX. This represents the maximum size
>>> that is allowed to be printed to the console for a single record.
>>>
>>> Rather than setting CONSOLE_LOG_MAX to "LOG_LINE_MAX + PREFIX_MAX"
>>> (1024), increase it to 4096. With a larger buffer size, multi-line
>>> records that are nearly LOG_LINE_MAX in length will have a better
>>> chance of being fully printed. (When formatting a record for the
>>> console, each line of a multi-line record is prepended with a copy
>>> of the prefix.)
>>>
>>> Signed-off-by: John Ogness <john.ogness@linutronix.de>
>>> Reviewed-by: Petr Mladek <pmladek@suse.com>
>>
>> Thanks for your patch!
>>
>> This increases kernel size by more than 3 KiB, which affects small
>> devices (e.g. SoCs with 10 MiB of SRAM inside).

Petr was concerned that this patch might raise issues for the small
devices.

>> Who is printing such long lines to the console?

Some printk users like to print large multi-line messages into a single
record. They can get pretty long. But since no one is complaining with
the current 1024, we can assume it is big enough.

For v4 I will return it back to 1024 bytes.

> BTW, printing a single line of 1024 characters to a serial console at
> 115200 bps takes almost 100 ms.

Yes. Although once we move to threaded printers, I don't think anyone
will care. Also, I think the netconsole will become quite attractive
when we move to threaded printers.

John Ogness