[PATCH v2 0/6] Function tracing support for pstore

[PATCH v2 0/6] Function tracing support for pstore

[Anton Vorontsov]

Hi all,

In v2:
- Do not introduce a separate 'persistent' tracer, but introduce an
  option to the existing 'function' tracer.

Rationale for this patch set:

With this support kernel can save functions call chain log into a
persistent ram buffer that can be decoded and dumped after reboot
through pstore filesystem. It can be used to determine what function
was last called before a hang or an unexpected reset (caused by, for
example, a buggy driver that abuses HW).

Here's a "nano howto", to get the idea:

 # mount -t debugfs debugfs /sys/kernel/debug/
 # cd /sys/kernel/debug/tracing
 # echo function > current_tracer
 # echo 1 > options/func_pstore
 # reboot -f
 [...]
 # mount -t pstore pstore /mnt/
 # tail /mnt/ftrace-ramoops
 0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
 0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
 0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
 0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
 0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0x37/0x40
 0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
 0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
 0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
 0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
 0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20

Mostly the code comes from trace_persistent.c driver found in the
Android git tree, written by Colin Cross <ccross@android.com>
(according to sign-off history). I reworked the driver a little bit,
and ported it to pstore subsystem.

---
 Documentation/ramoops.txt      |   25 +++++++++
 fs/pstore/Kconfig              |   12 +++++
 fs/pstore/Makefile             |    6 +++
 fs/pstore/ftrace.c             |   35 +++++++++++++
 fs/pstore/inode.c              |  111 ++++++++++++++++++++++++++++++++++++++--
 fs/pstore/internal.h           |   49 ++++++++++++++++++
 fs/pstore/platform.c           |   12 ++++-
 fs/pstore/ram.c                |   54 ++++++++++++++-----
 include/linux/pstore.h         |   13 +++++
 include/linux/pstore_ram.h     |    1 +
 kernel/trace/trace.c           |    7 +--
 kernel/trace/trace_functions.c |   25 +++++++--
 12 files changed, 325 insertions(+), 25 deletions(-)

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com

[PATCH 1/6] tracing: Fix initialization failure path in tracing_set_tracer()

[Anton Vorontsov]

If tracer->init() fails, current code will leave current_tracer pointing
to an unusable tracer, which at best makes 'current_tracer' report
inaccurate value.

Fix the issue by pointing current_tracer to nop tracer, and only update
current_tracer with the new one after all the initialization succeeds.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 kernel/trace/trace.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fa070..7647d33 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
 	}
 	destroy_trace_option_files(topts);
 
-	current_trace = t;
+	current_trace = &nop_trace;
 
-	topts = create_trace_option_files(current_trace);
-	if (current_trace->use_max_tr) {
+	topts = create_trace_option_files(t);
+	if (t->use_max_tr) {
 		int cpu;
 		/* we need to make per cpu buffer sizes equivalent */
 		for_each_tracing_cpu(cpu) {
@@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
 			goto out;
 	}
 
+	current_trace = t;
 	trace_branch_enable(tr);
  out:
 	mutex_unlock(&trace_types_lock);
-- 
1.7.10.4

[PATCH 2/6] pstore: Introduce write_buf backend callback

[Anton Vorontsov]

For function tracing we need to stop using pstore.buf directly, since
in a tracing callback we can't use spinlocks, and thus we can't safely
use the global buffer.

With write_buf callback, backends no longer need to access pstore.buf
directly, and thus we can pass any buffers (e.g. allocated on stack).

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/platform.c   |   10 ++++++++++
 include/linux/pstore.h |    4 ++++
 2 files changed, 14 insertions(+)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index be4614f..e7c0a52 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -198,6 +198,14 @@ static void pstore_register_console(void)
 static void pstore_register_console(void) {}
 #endif
 
+static int pstore_write_compat(enum pstore_type_id type,
+			       enum kmsg_dump_reason reason,
+			       u64 *id, unsigned int part,
+			       size_t size, struct pstore_info *psi)
+{
+	return psi->write_buf(type, reason, id, part, psinfo->buf, size, psi);
+}
+
 /*
  * platform specific persistent storage driver registers with
  * us here. If pstore is already mounted, call the platform
@@ -222,6 +230,8 @@ int pstore_register(struct pstore_info *psi)
 		return -EINVAL;
 	}
 
+	if (!psi->write)
+		psi->write = pstore_write_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
 	spin_unlock(&pstore_lock);
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index 1bd014b..b107484 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -48,6 +48,10 @@ struct pstore_info {
 	int		(*write)(enum pstore_type_id type,
 			enum kmsg_dump_reason reason, u64 *id,
 			unsigned int part, size_t size, struct pstore_info *psi);
+	int		(*write_buf)(enum pstore_type_id type,
+			enum kmsg_dump_reason reason, u64 *id,
+			unsigned int part, const char *buf, size_t size,
+			struct pstore_info *psi);
 	int		(*erase)(enum pstore_type_id type, u64 id,
 			struct pstore_info *psi);
 	void		*data;
-- 
1.7.10.4

[PATCH 3/6] pstore: Add persistent function tracing

[Anton Vorontsov]

With this support kernel can save function call chain log into a
persistent ram buffer that can be decoded and dumped after reboot
through pstore filesystem. It can be used to determine what function
was last called before a reset or panic.

We store the log in a binary format and then decode it at read time.

p.s.
Mostly the code comes from trace_persistent.c driver found in the
Android git tree, written by Colin Cross <ccross@android.com>
(according to sign-off history). I reworked the driver a little bit,
and ported it to pstore.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/Kconfig      |   12 ++++++
 fs/pstore/Makefile     |    6 +++
 fs/pstore/ftrace.c     |   35 +++++++++++++++
 fs/pstore/inode.c      |  111 ++++++++++++++++++++++++++++++++++++++++++++++--
 fs/pstore/internal.h   |   49 +++++++++++++++++++++
 fs/pstore/platform.c   |    2 +-
 include/linux/pstore.h |    9 ++++
 7 files changed, 219 insertions(+), 5 deletions(-)
 create mode 100644 fs/pstore/ftrace.c

diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
index d044de6..d39bb5c 100644
--- a/fs/pstore/Kconfig
+++ b/fs/pstore/Kconfig
@@ -19,6 +19,18 @@ config PSTORE_CONSOLE
 	  When the option is enabled, pstore will log all kernel
 	  messages, even if no oops or panic happened.
 
+config PSTORE_FTRACE
+	bool "Persistent function tracer"
+	depends on PSTORE
+	depends on FUNCTION_TRACER
+	help
+	  With this option kernel traces function calls into a persistent
+	  ram buffer that can be decoded and dumped after reboot through
+	  pstore filesystem. It can be used to determine what function
+	  was last called before a reset or panic.
+
+	  If unsure, say N.
+
 config PSTORE_RAM
 	tristate "Log panic/oops to a RAM buffer"
 	depends on PSTORE
diff --git a/fs/pstore/Makefile b/fs/pstore/Makefile
index 278a44e..cc6aa3d 100644
--- a/fs/pstore/Makefile
+++ b/fs/pstore/Makefile
@@ -7,4 +7,10 @@ obj-y += pstore.o
 pstore-objs += inode.o platform.o
 
 ramoops-objs += ram.o ram_core.o
+
+ifeq ($(CONFIG_PSTORE_FTRACE),y)
+ramoops-objs += ftrace.o
+CFLAGS_REMOVE_ftrace.o = -pg
+endif
+
 obj-$(CONFIG_PSTORE_RAM)	+= ramoops.o
diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
new file mode 100644
index 0000000..8e2ef07
--- /dev/null
+++ b/fs/pstore/ftrace.c
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2012  Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/compiler.h>
+#include <linux/irqflags.h>
+#include <linux/percpu.h>
+#include <linux/smp.h>
+#include <linux/atomic.h>
+#include <asm/barrier.h>
+#include "internal.h"
+
+void pstore_ftrace_call(unsigned long ip, unsigned long parent_ip)
+{
+	struct pstore_ftrace_record rec = {};
+
+	if (unlikely(oops_in_progress))
+		return;
+
+	rec.ip = ip;
+	rec.parent_ip = parent_ip;
+	pstore_ftrace_encode_cpu(&rec, raw_smp_processor_id());
+	psinfo->write_buf(PSTORE_TYPE_FTRACE, 0, NULL, 0, (void *)&rec,
+			  sizeof(rec), psinfo);
+}
diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 45bff54..4ab572e 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -27,6 +27,7 @@
 #include <linux/list.h>
 #include <linux/string.h>
 #include <linux/mount.h>
+#include <linux/seq_file.h>
 #include <linux/ramfs.h>
 #include <linux/parser.h>
 #include <linux/sched.h>
@@ -52,18 +53,117 @@ struct pstore_private {
 	char	data[];
 };
 
+struct pstore_ftrace_seq_data {
+	const void *ptr;
+	size_t off;
+	size_t size;
+};
+
+#define REC_SIZE sizeof(struct pstore_ftrace_record)
+
+static void *pstore_ftrace_seq_start(struct seq_file *s, loff_t *pos)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return NULL;
+
+	data->off = ps->size % REC_SIZE;
+	data->off += *pos * REC_SIZE;
+	if (data->off + REC_SIZE > ps->size) {
+		kfree(data);
+		return NULL;
+	}
+
+	return data;
+
+}
+
+static void pstore_ftrace_seq_stop(struct seq_file *s, void *v)
+{
+	kfree(v);
+}
+
+static void *pstore_ftrace_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data = v;
+
+	data->off += REC_SIZE;
+	if (data->off + REC_SIZE > ps->size)
+		return NULL;
+
+	(*pos)++;
+	return data;
+}
+
+static int pstore_ftrace_seq_show(struct seq_file *s, void *v)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data = v;
+	struct pstore_ftrace_record *rec = (void *)(ps->data + data->off);
+
+	seq_printf(s, "%d %08lx  %08lx  %pf <- %pF\n",
+		pstore_ftrace_decode_cpu(rec), rec->ip, rec->parent_ip,
+		(void *)rec->ip, (void *)rec->parent_ip);
+
+	return 0;
+}
+
+static const struct seq_operations pstore_ftrace_seq_ops = {
+	.start	= pstore_ftrace_seq_start,
+	.next	= pstore_ftrace_seq_next,
+	.stop	= pstore_ftrace_seq_stop,
+	.show	= pstore_ftrace_seq_show,
+};
+
 static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
 						size_t count, loff_t *ppos)
 {
-	struct pstore_private *ps = file->private_data;
+	struct seq_file *sf = file->private_data;
+	struct pstore_private *ps = sf->private;
 
+	if (ps->type == PSTORE_TYPE_FTRACE)
+		return seq_read(file, userbuf, count, ppos);
 	return simple_read_from_buffer(userbuf, count, ppos, ps->data, ps->size);
 }
 
+static int pstore_file_open(struct inode *inode, struct file *file)
+{
+	struct pstore_private *ps = inode->i_private;
+	struct seq_file *sf;
+	int err;
+	const struct seq_operations *sops = NULL;
+
+	if (ps->type == PSTORE_TYPE_FTRACE)
+		sops = &pstore_ftrace_seq_ops;
+
+	err = seq_open(file, sops);
+	if (err < 0)
+		return err;
+
+	sf = file->private_data;
+	sf->private = ps;
+
+	return 0;
+}
+
+static loff_t pstore_file_llseek(struct file *file, loff_t off, int origin)
+{
+	struct seq_file *sf = file->private_data;
+
+	if (sf->op)
+		return seq_lseek(file, off, origin);
+	return default_llseek(file, off, origin);
+}
+
 static const struct file_operations pstore_file_operations = {
-	.open	= simple_open,
-	.read	= pstore_file_read,
-	.llseek	= default_llseek,
+	.open		= pstore_file_open,
+	.read		= pstore_file_read,
+	.llseek		= pstore_file_llseek,
+	.release	= seq_release,
 };
 
 /*
@@ -215,6 +315,9 @@ int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id,
 	case PSTORE_TYPE_CONSOLE:
 		sprintf(name, "console-%s", psname);
 		break;
+	case PSTORE_TYPE_FTRACE:
+		sprintf(name, "ftrace-%s", psname);
+		break;
 	case PSTORE_TYPE_MCE:
 		sprintf(name, "mce-%s-%lld", psname, id);
 		break;
diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
index 3bde461..6e09673 100644
--- a/fs/pstore/internal.h
+++ b/fs/pstore/internal.h
@@ -1,6 +1,55 @@
+#ifndef __PSTORE_INTERNAL_H__
+#define __PSTORE_INTERNAL_H__
+
+#include <linux/pstore.h>
+
+#if NR_CPUS <= 2 && defined(CONFIG_ARM_THUMB)
+#define PSTORE_CPU_IN_IP 0x1
+#elif NR_CPUS <= 4 && defined(CONFIG_ARM)
+#define PSTORE_CPU_IN_IP 0x3
+#endif
+
+struct pstore_ftrace_record {
+	unsigned long ip;
+	unsigned long parent_ip;
+#ifndef PSTORE_CPU_IN_IP
+	unsigned int cpu;
+#endif
+};
+
+static inline void
+pstore_ftrace_encode_cpu(struct pstore_ftrace_record *rec, unsigned int cpu)
+{
+#ifndef PSTORE_CPU_IN_IP
+	rec->cpu = cpu;
+#else
+	rec->ip |= cpu;
+#endif
+}
+
+static inline unsigned int
+pstore_ftrace_decode_cpu(struct pstore_ftrace_record *rec)
+{
+#ifndef PSTORE_CPU_IN_IP
+	return rec->cpu;
+#else
+	return rec->ip & PSTORE_CPU_IN_IP;
+#endif
+}
+
+#ifdef CONFIG_PSTORE_FTRACE
+extern void pstore_register_ftrace(void);
+#else
+static inline void pstore_register_ftrace(void) {}
+#endif
+
+extern struct pstore_info *psinfo;
+
 extern void	pstore_set_kmsg_bytes(int);
 extern void	pstore_get_records(int);
 extern int	pstore_mkfile(enum pstore_type_id, char *psname, u64 id,
 			      char *data, size_t size,
 			      struct timespec time, struct pstore_info *psi);
 extern int	pstore_is_mounted(void);
+
+#endif
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index e7c0a52..86af54e 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -61,7 +61,7 @@ static DECLARE_WORK(pstore_work, pstore_dowork);
  * calls to pstore_register()
  */
 static DEFINE_SPINLOCK(pstore_lock);
-static struct pstore_info *psinfo;
+struct pstore_info *psinfo;
 
 static char *backend;
 
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index b107484..120443b 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -30,6 +30,7 @@ enum pstore_type_id {
 	PSTORE_TYPE_DMESG	= 0,
 	PSTORE_TYPE_MCE		= 1,
 	PSTORE_TYPE_CONSOLE	= 2,
+	PSTORE_TYPE_FTRACE	= 3,
 	PSTORE_TYPE_UNKNOWN	= 255
 };
 
@@ -57,6 +58,14 @@ struct pstore_info {
 	void		*data;
 };
 
+
+#ifdef CONFIG_PSTORE_FTRACE
+extern void pstore_ftrace_call(unsigned long ip, unsigned long parent_ip);
+#else
+static inline void pstore_ftrace_call(unsigned long ip, unsigned long parent_ip)
+{ }
+#endif
+
 #ifdef CONFIG_PSTORE
 extern int pstore_register(struct pstore_info *);
 #else
-- 
1.7.10.4

[PATCH 4/6] tracing/function: Introduce persistent trace option

[Anton Vorontsov]

This patch introduces 'func_ptrace' option, now available in
/sys/kernel/debug/tracing/options when function tracer
is selected.

The patch also adds some tiny code that calls back to pstore
to record the trace. The callback is no-op when PSTORE=n.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 kernel/trace/trace_functions.c |   25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index c7b0c6a..269627c 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -13,6 +13,7 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
+#include <linux/pstore.h>
 #include <linux/fs.h>
 
 #include "trace.h"
@@ -74,6 +75,14 @@ function_trace_call_preempt_only(unsigned long ip, unsigned long parent_ip)
 	preempt_enable_notrace();
 }
 
+/* Our two options */
+enum {
+	TRACE_FUNC_OPT_STACK	= 0x1,
+	TRACE_FUNC_OPT_PSTORE	= 0x2,
+};
+
+static struct tracer_flags func_flags;
+
 static void
 function_trace_call(unsigned long ip, unsigned long parent_ip)
 {
@@ -97,6 +106,12 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
 	disabled = atomic_inc_return(&data->disabled);
 
 	if (likely(disabled == 1)) {
+		/*
+		 * So far tracing doesn't support multiple buffers, so
+		 * we make an explicit call for now.
+		 */
+		if (unlikely(func_flags.val & TRACE_FUNC_OPT_PSTORE))
+			pstore_ftrace_call(ip, parent_ip);
 		pc = preempt_count();
 		trace_function(tr, ip, parent_ip, flags, pc);
 	}
@@ -158,15 +173,13 @@ static struct ftrace_ops trace_stack_ops __read_mostly =
 	.flags = FTRACE_OPS_FL_GLOBAL,
 };
 
-/* Our two options */
-enum {
-	TRACE_FUNC_OPT_STACK = 0x1,
-};
-
 static struct tracer_opt func_opts[] = {
 #ifdef CONFIG_STACKTRACE
 	{ TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
 #endif
+#ifdef CONFIG_PSTORE_FTRACE
+	{ TRACER_OPT(func_pstore, TRACE_FUNC_OPT_PSTORE) },
+#endif
 	{ } /* Always set a last empty entry */
 };
 
@@ -219,6 +232,8 @@ static int func_set_flag(u32 old_flags, u32 bit, int set)
 
 		return 0;
 	}
+	if (bit == TRACE_FUNC_OPT_PSTORE)
+		return 0;
 
 	return -EINVAL;
 }
-- 
1.7.10.4

[PATCH 5/6] pstore/ram: Convert to write_buf callback

[Anton Vorontsov]

Don't use pstore.buf directly, instead convert the code to write_buf callback
which passes a pointer to a buffer as an argument.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/ram.c |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index c7acf94..96dbd1e 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -168,11 +168,12 @@ static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz)
 	return len;
 }
 
-static int ramoops_pstore_write(enum pstore_type_id type,
-				enum kmsg_dump_reason reason,
-				u64 *id,
-				unsigned int part,
-				size_t size, struct pstore_info *psi)
+
+static int ramoops_pstore_write_buf(enum pstore_type_id type,
+				    enum kmsg_dump_reason reason,
+				    u64 *id, unsigned int part,
+				    const char *buf, size_t size,
+				    struct pstore_info *psi)
 {
 	struct ramoops_context *cxt = psi->data;
 	struct persistent_ram_zone *prz = cxt->przs[cxt->dump_write_cnt];
@@ -181,7 +182,7 @@ static int ramoops_pstore_write(enum pstore_type_id type,
 	if (type == PSTORE_TYPE_CONSOLE) {
 		if (!cxt->cprz)
 			return -ENOMEM;
-		persistent_ram_write(cxt->cprz, cxt->pstore.buf, size);
+		persistent_ram_write(cxt->cprz, buf, size);
 		return 0;
 	}
 
@@ -210,7 +211,7 @@ static int ramoops_pstore_write(enum pstore_type_id type,
 	hlen = ramoops_write_kmsg_hdr(prz);
 	if (size + hlen > prz->buffer_size)
 		size = prz->buffer_size - hlen;
-	persistent_ram_write(prz, cxt->pstore.buf, size);
+	persistent_ram_write(prz, buf, size);
 
 	cxt->dump_write_cnt = (cxt->dump_write_cnt + 1) % cxt->max_dump_cnt;
 
@@ -248,7 +249,7 @@ static struct ramoops_context oops_cxt = {
 		.name	= "ramoops",
 		.open	= ramoops_pstore_open,
 		.read	= ramoops_pstore_read,
-		.write	= ramoops_pstore_write,
+		.write_buf	= ramoops_pstore_write_buf,
 		.erase	= ramoops_pstore_erase,
 	},
 };
-- 
1.7.10.4

[PATCH 6/6] pstore/ram: Add ftrace messages handling

[Anton Vorontsov]

The ftrace log size is configurable via ramoops.ftrace_size
module option, and the log itself is available via
<pstore-mount>/ftrace-ramoops file.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 Documentation/ramoops.txt  |   25 +++++++++++++++++++++++++
 fs/pstore/ram.c            |   37 +++++++++++++++++++++++++++++++++----
 include/linux/pstore_ram.h |    1 +
 3 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
index 59a74a8..197ad59 100644
--- a/Documentation/ramoops.txt
+++ b/Documentation/ramoops.txt
@@ -94,3 +94,28 @@ timestamp and a new line. The dump then continues with the actual data.
 The dump data can be read from the pstore filesystem. The format for these
 files is "dmesg-ramoops-N", where N is the record number in memory. To delete
 a stored record from RAM, simply unlink the respective pstore file.
+
+5. Persistent function tracing
+
+Persistent function tracing might be useful for debugging software or hardware
+related hangs. The functions call chain log is stored in a "ftrace-ramoops"
+file. Here is an example of usage:
+
+ # mount -t debugfs debugfs /sys/kernel/debug/
+ # cd /sys/kernel/debug/tracing
+ # echo function > current_tracer
+ # echo 1 > options/func_pstore
+ # reboot -f
+ [...]
+ # mount -t pstore pstore /mnt/
+ # tail /mnt/ftrace-ramoops
+ 0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
+ 0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
+ 0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
+ 0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
+ 0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0x37/0x40
+ 0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
+ 0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
+ 0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
+ 0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
+ 0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20
diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 96dbd1e..018d895 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -45,6 +45,10 @@ static ulong ramoops_console_size = MIN_MEM_SIZE;
 module_param_named(console_size, ramoops_console_size, ulong, 0400);
 MODULE_PARM_DESC(console_size, "size of kernel console log");
 
+static ulong ramoops_ftrace_size = MIN_MEM_SIZE;
+module_param_named(ftrace_size, ramoops_ftrace_size, ulong, 0400);
+MODULE_PARM_DESC(ftrace_size, "size of ftrace log");
+
 static ulong mem_address;
 module_param(mem_address, ulong, 0400);
 MODULE_PARM_DESC(mem_address,
@@ -68,16 +72,19 @@ MODULE_PARM_DESC(ramoops_ecc,
 struct ramoops_context {
 	struct persistent_ram_zone **przs;
 	struct persistent_ram_zone *cprz;
+	struct persistent_ram_zone *fprz;
 	phys_addr_t phys_addr;
 	unsigned long size;
 	size_t record_size;
 	size_t console_size;
+	size_t ftrace_size;
 	int dump_oops;
 	bool ecc;
 	unsigned int max_dump_cnt;
 	unsigned int dump_write_cnt;
 	unsigned int dump_read_cnt;
 	unsigned int console_read_cnt;
+	unsigned int ftrace_read_cnt;
 	struct pstore_info pstore;
 };
 
@@ -136,6 +143,9 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 		prz = ramoops_get_next_prz(&cxt->cprz, &cxt->console_read_cnt,
 					   1, id, type, PSTORE_TYPE_CONSOLE, 0);
 	if (!prz)
+		prz = ramoops_get_next_prz(&cxt->fprz, &cxt->ftrace_read_cnt,
+					   1, id, type, PSTORE_TYPE_FTRACE, 0);
+	if (!prz)
 		return 0;
 
 	/* TODO(kees): Bogus time for the moment. */
@@ -184,6 +194,11 @@ static int ramoops_pstore_write_buf(enum pstore_type_id type,
 			return -ENOMEM;
 		persistent_ram_write(cxt->cprz, buf, size);
 		return 0;
+	} else if (type == PSTORE_TYPE_FTRACE) {
+		if (!cxt->fprz)
+			return -ENOMEM;
+		persistent_ram_write(cxt->fprz, buf, size);
+		return 0;
 	}
 
 	if (type != PSTORE_TYPE_DMESG)
@@ -233,6 +248,9 @@ static int ramoops_pstore_erase(enum pstore_type_id type, u64 id,
 	case PSTORE_TYPE_CONSOLE:
 		prz = cxt->cprz;
 		break;
+	case PSTORE_TYPE_FTRACE:
+		prz = cxt->fprz;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -346,7 +364,8 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	if (cxt->max_dump_cnt)
 		goto fail_out;
 
-	if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size)) {
+	if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size &&
+			!pdata->ftrace_size)) {
 		pr_err("The memory size and the record/console size must be "
 			"non-zero\n");
 		goto fail_out;
@@ -355,18 +374,20 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	pdata->mem_size = rounddown_pow_of_two(pdata->mem_size);
 	pdata->record_size = rounddown_pow_of_two(pdata->record_size);
 	pdata->console_size = rounddown_pow_of_two(pdata->console_size);
+	pdata->ftrace_size = rounddown_pow_of_two(pdata->ftrace_size);
 
 	cxt->dump_read_cnt = 0;
 	cxt->size = pdata->mem_size;
 	cxt->phys_addr = pdata->mem_address;
 	cxt->record_size = pdata->record_size;
 	cxt->console_size = pdata->console_size;
+	cxt->ftrace_size = pdata->ftrace_size;
 	cxt->dump_oops = pdata->dump_oops;
 	cxt->ecc = pdata->ecc;
 
 	paddr = cxt->phys_addr;
 
-	dump_mem_sz = cxt->size - cxt->console_size;
+	dump_mem_sz = cxt->size - cxt->console_size - cxt->ftrace_size;
 	err = ramoops_init_przs(dev, cxt, &paddr, dump_mem_sz);
 	if (err)
 		goto fail_out;
@@ -375,9 +396,14 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	if (err)
 		goto fail_init_cprz;
 
-	if (!cxt->przs && !cxt->cprz) {
+	err = ramoops_init_prz(dev, cxt, &cxt->fprz, &paddr, cxt->ftrace_size);
+	if (err)
+		goto fail_init_fprz;
+
+	if (!cxt->przs && !cxt->cprz && !cxt->fprz) {
 		pr_err("memory size too small, minimum is %lu\n",
-			cxt->console_size + cxt->record_size);
+			cxt->console_size + cxt->record_size +
+			cxt->ftrace_size);
 		goto fail_cnt;
 	}
 
@@ -424,6 +450,8 @@ fail_clear:
 	cxt->pstore.bufsize = 0;
 	cxt->max_dump_cnt = 0;
 fail_cnt:
+	kfree(cxt->fprz);
+fail_init_fprz:
 	kfree(cxt->cprz);
 fail_init_cprz:
 	ramoops_free_przs(cxt);
@@ -478,6 +506,7 @@ static int __init ramoops_init(void)
 		dummy_data->mem_address = mem_address;
 		dummy_data->record_size = record_size;
 		dummy_data->console_size = ramoops_console_size;
+		dummy_data->ftrace_size = ramoops_ftrace_size;
 		dummy_data->dump_oops = dump_oops;
 		dummy_data->ecc = ramoops_ecc;
 		dummy = platform_create_bundle(&ramoops_driver, ramoops_probe,
diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
index 2470bb5..368da13 100644
--- a/include/linux/pstore_ram.h
+++ b/include/linux/pstore_ram.h
@@ -75,6 +75,7 @@ struct ramoops_platform_data {
 	unsigned long	mem_address;
 	unsigned long	record_size;
 	unsigned long	console_size;
+	unsigned long	ftrace_size;
 	int		dump_oops;
 	bool		ecc;
 };
-- 
1.7.10.4

Re: [PATCH v2 0/6] Function tracing support for pstore

[Greg Kroah-Hartman]

On Fri, Jun 15, 2012 at 10:07:00AM -0700, Anton Vorontsov wrote:
> Hi all,
> 
> In v2:
> - Do not introduce a separate 'persistent' tracer, but introduce an
>   option to the existing 'function' tracer.
> 
> Rationale for this patch set:
> 
> With this support kernel can save functions call chain log into a
> persistent ram buffer that can be decoded and dumped after reboot
> through pstore filesystem. It can be used to determine what function
> was last called before a hang or an unexpected reset (caused by, for
> example, a buggy driver that abuses HW).
> 
> Here's a "nano howto", to get the idea:
> 
>  # mount -t debugfs debugfs /sys/kernel/debug/
>  # cd /sys/kernel/debug/tracing
>  # echo function > current_tracer
>  # echo 1 > options/func_pstore
>  # reboot -f
>  [...]
>  # mount -t pstore pstore /mnt/
>  # tail /mnt/ftrace-ramoops
>  0 ffffffff8101ea64  ffffffff8101bcda  native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
>  0 ffffffff8101ea44  ffffffff8101bcf6  native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
>  0 ffffffff81020084  ffffffff8101a4b5  hpet_disable <- native_machine_shutdown+0x75/0x90
>  0 ffffffff81005f94  ffffffff8101a4bb  iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
>  0 ffffffff8101a6a1  ffffffff8101a437  native_machine_emergency_restart <- native_machine_restart+0x37/0x40
>  0 ffffffff811f9876  ffffffff8101a73a  acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
>  0 ffffffff8101a514  ffffffff8101a772  mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
>  0 ffffffff811d9c54  ffffffff8101a7a0  __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
>  0 ffffffff811d9c34  ffffffff811d9c80  __delay <- __const_udelay+0x30/0x40
>  0 ffffffff811d9d14  ffffffff811d9c3f  delay_tsc <- __delay+0xf/0x20
> 
> Mostly the code comes from trace_persistent.c driver found in the
> Android git tree, written by Colin Cross <ccross@android.com>
> (according to sign-off history). I reworked the driver a little bit,
> and ported it to pstore subsystem.


This looks fine to me, but as it touches pstore and tracing code, I
can't apply it without acks from the relevant maintainers/owners.

thanks,

greg k-h

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Luck, Tony]

> We store the log in a binary format and then decode it at read time.

What are the advantages of this compared to creating the human
readable text and saving a blob of text?

What does this "binary format" look like?  Will it ever change?
Remember that we may reboot to a different kernel - so we have
to be really sure that the newer (or older) version can do the decode.

-Tony

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Steven Rostedt]

On Fri, 2012-06-15 at 21:40 +0000, Luck, Tony wrote:
> > We store the log in a binary format and then decode it at read time.
> 
> What are the advantages of this compared to creating the human
> readable text and saving a blob of text?

With function tracing the impact to performance is tremendous. Just
recording two long words is a 130% hit to performance. Now multiply that
to recording strings.

> 
> What does this "binary format" look like?  Will it ever change?
> Remember that we may reboot to a different kernel - so we have
> to be really sure that the newer (or older) version can do the decode.

Good question.

-- Steve

Re: [PATCH 1/6] tracing: Fix initialization failure path in tracing_set_tracer()

[Steven Rostedt]

On Fri, 2012-06-15 at 10:08 -0700, Anton Vorontsov wrote:
> If tracer->init() fails, current code will leave current_tracer pointing
> to an unusable tracer, which at best makes 'current_tracer' report
> inaccurate value.
> 
> Fix the issue by pointing current_tracer to nop tracer, and only update
> current_tracer with the new one after all the initialization succeeds.
> 
> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>

Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

> ---
>  kernel/trace/trace.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a7fa070..7647d33 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
>  	}
>  	destroy_trace_option_files(topts);
>  
> -	current_trace = t;
> +	current_trace = &nop_trace;
>  
> -	topts = create_trace_option_files(current_trace);
> -	if (current_trace->use_max_tr) {
> +	topts = create_trace_option_files(t);
> +	if (t->use_max_tr) {
>  		int cpu;
>  		/* we need to make per cpu buffer sizes equivalent */
>  		for_each_tracing_cpu(cpu) {
> @@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
>  			goto out;
>  	}
>  
> +	current_trace = t;
>  	trace_branch_enable(tr);
>   out:
>  	mutex_unlock(&trace_types_lock);

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Luck, Tony]

> With function tracing the impact to performance is tremendous. Just
> recording two long words is a 130% hit to performance. Now multiply that
> to recording strings.

If pstore is writing to a flash based backend - then there will be many
milli-seconds of delay. I think the time taken to convert from binary to
ascii would be insignificant.

-Tony

Re: [PATCH 3/6] pstore: Add persistent function tracing

[Colin Cross]

On Fri, Jun 15, 2012 at 3:00 PM, Luck, Tony <tony.luck@intel.com> wrote:
>> With function tracing the impact to performance is tremendous. Just
>> recording two long words is a 130% hit to performance. Now multiply that
>> to recording strings.
>
> If pstore is writing to a flash based backend - then there will be many
> milli-seconds of delay. I think the time taken to convert from binary to
> ascii would be insignificant.

Function tracing into flash would be silly, adding milliseconds of
overhead to every function call is enormous.  The normal use case for
this is tracing to persistent ram, and even the difference between 2
and 3 words in the binary format was noticeable.  Converting to ascii
would expand 2 words to at least 20 words, making the entire feature
useless.

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Steven Rostedt]

On Fri, 2012-06-15 at 22:00 +0000, Luck, Tony wrote:
> > With function tracing the impact to performance is tremendous. Just
> > recording two long words is a 130% hit to performance. Now multiply that
> > to recording strings.
> 
> If pstore is writing to a flash based backend - then there will be many
> milli-seconds of delay. I think the time taken to convert from binary to
> ascii would be insignificant.

milli-seconds for recording? This would cripple the kernel. On slow
machines, incorporating lockdep into function tracing (and other debug
options) causes the system to live lock. Tracing the timer interrupt
took so long that by the time it finished, the next timer triggered
again.

Heck, today you can pretty much live lock most machines if you enabled
the option 'func_stack_trace' while function tracing without filtering.
You may be able to get your system back again, but it usually takes
several seconds to acknowledge each key stroke (if you're lucky, but we
all know *you* are ;-)


If we are talking about milli-seconds to record. Then this is a no go,
as it wont be worth adding. I'm thinking their buffering system is much
faster than that today, as they have shown examples already.

-- Steve

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Luck, Tony]

> milli-seconds for recording? This would cripple the kernel. On slow
> machines, incorporating lockdep into function tracing (and other debug
> options) causes the system to live lock. Tracing the timer interrupt
> took so long that by the time it finished, the next timer triggered
> again.

Ah - I think I misunderstood how this works ... I thought the function
trace was taken at some point in the crash/shutdown path.  Now I see
that it is being generated repeatedly as the kernel runs ... with the
idea that if a hang happens, you can see the last call trace that was
successful.

Ok then - clearly this is only useful with a ram backend for pstore.

Binary makes sense too - but I'll stick with my comment that a different
kernel must be able to do the decode. Or we need to spell out clearly
that you must have the same, or compatible kernel booted to make any
sense of the saved ftrace record.

-Tony

Re: [PATCH 3/6] pstore: Add persistent function tracing

[Colin Cross]

On Fri, Jun 15, 2012 at 3:19 PM, Luck, Tony <tony.luck@intel.com> wrote:
>> milli-seconds for recording? This would cripple the kernel. On slow
>> machines, incorporating lockdep into function tracing (and other debug
>> options) causes the system to live lock. Tracing the timer interrupt
>> took so long that by the time it finished, the next timer triggered
>> again.
>
> Ah - I think I misunderstood how this works ... I thought the function
> trace was taken at some point in the crash/shutdown path.  Now I see
> that it is being generated repeatedly as the kernel runs ... with the
> idea that if a hang happens, you can see the last call trace that was
> successful.
>
> Ok then - clearly this is only useful with a ram backend for pstore.
>
> Binary makes sense too - but I'll stick with my comment that a different
> kernel must be able to do the decode. Or we need to spell out clearly
> that you must have the same, or compatible kernel booted to make any
> sense of the saved ftrace record.

The decode also converts PCs to symbols, so for all the data to be
useful you have to boot the exact same kernel.  You could
theoretically boot a different kernel with a compatible format, but
you would have to manually extract the PCs from the dump and addr2line
them against the correct vmlinux, which is probably more trouble than
it's worth.  Also, the binary data is stored inside a pstore_ram
ringbuffer that may change formats between kernels.  I would suggest
documenting that this is only supposed to work booting back to the
same kernel.

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Steven Rostedt]

On Fri, 2012-06-15 at 22:19 +0000, Luck, Tony wrote:

> Binary makes sense too - but I'll stick with my comment that a different
> kernel must be able to do the decode. Or we need to spell out clearly
> that you must have the same, or compatible kernel booted to make any
> sense of the saved ftrace record.

I 100% agree here. I haven't looked at how the data gets stored, but it
should definitely be consistent across kernels.

Maybe store metadata in the persistent storage that explains how to
parse the binary data? Similar to /debug/tracing/events/ftrace/function/format
is done.


-- Steve

RE: [PATCH 3/6] pstore: Add persistent function tracing

[Luck, Tony]

> The decode also converts PCs to symbols, so for all the data to be
> useful you have to boot the exact same kernel

With the same modules loaded at the same addresses (if your traces
are going to include paths through loaded modules).

Perhaps include a hash of the kernel symbol table so the decoder
can tell whether it has any hope of making sense of the trace?
[Compute the hash at boot and when modules are loaded/unloaded,
then store in a header section of the binary ftrace record]

-Tony

Re: [PATCH 3/6] pstore: Add persistent function tracing

[Steven Rostedt]

On Fri, 2012-06-15 at 15:23 -0700, Colin Cross wrote:

> The decode also converts PCs to symbols, so for all the data to be
> useful you have to boot the exact same kernel.  You could
> theoretically boot a different kernel with a compatible format, but
> you would have to manually extract the PCs from the dump and addr2line
> them against the correct vmlinux, which is probably more trouble than
> it's worth.  Also, the binary data is stored inside a pstore_ram
> ringbuffer that may change formats between kernels.  I would suggest
> documenting that this is only supposed to work booting back to the
> same kernel.

OK, I'm fine with this too, if it is well documented that the same
kernel must be used. Make it similar to hibernating the box. That is,
you don't want to boot into a different kernel after you shutdown by
hibernating to the hard drive.

-- Steve