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From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd@lists.infradead.org
Subject: [PATCH next v4 02/15] mtd: mtdoops: synchronize kmsg_dumper
Date: Wed,  3 Mar 2021 11:15:15 +0100	[thread overview]
Message-ID: <20210303101528.29901-3-john.ogness@linutronix.de> (raw)
In-Reply-To: <20210303101528.29901-1-john.ogness@linutronix.de>

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).

An atomic bit (rather than a spinlock) was chosen so that no
scheduling or preemption side-effects would be introduced. The MTD
kmsg_dumper may dump directly or it may be delayed (via scheduled
work). Depending on the context, different MTD callbacks are used.
For example, mtd_write() expects to be called in a non-atomic
context and may take a mutex.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 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


  parent reply	other threads:[~2021-03-03 14:33 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-03 10:15 [PATCH next v4 00/15] printk: remove logbuf_lock John Ogness
2021-03-03 10:15 ` [PATCH next v4 01/15] um: synchronize kmsg_dumper John Ogness
2021-03-03 10:15 ` John Ogness [this message]
2021-03-11  9:50   ` [PATCH next v4 02/15] mtd: mtdoops: " Miquel Raynal
2021-03-03 10:15 ` [PATCH next v4 03/15] printk: limit second loop of syslog_print_all John Ogness
2021-03-03 10:15 ` [PATCH next v4 04/15] printk: kmsg_dump: remove unused fields John Ogness
2021-03-03 10:15 ` [PATCH next v4 05/15] printk: refactor kmsg_dump_get_buffer() John Ogness
2021-03-03 10:15 ` [PATCH next v4 06/15] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code John Ogness
2021-03-03 10:15 ` [PATCH next v4 07/15] printk: introduce CONSOLE_LOG_MAX John Ogness
2021-03-03 13:35   ` Petr Mladek
2021-03-03 10:15 ` [PATCH next v4 08/15] printk: use seqcount_latch for clear_seq John Ogness
2021-03-03 10:15 ` [PATCH next v4 09/15] printk: use atomic64_t for devkmsg_user.seq John Ogness
2021-03-03 10:15 ` [PATCH next v4 10/15] printk: add syslog_lock John Ogness
2021-03-03 10:15 ` [PATCH next v4 11/15] printk: kmsg_dumper: remove @active field John Ogness
2021-03-03 10:15 ` [PATCH next v4 12/15] printk: introduce a kmsg_dump iterator John Ogness
2021-03-03 13:48   ` Petr Mladek
2021-03-03 10:15 ` [PATCH next v4 13/15] printk: remove logbuf_lock John Ogness
2021-03-03 10:15 ` [PATCH next v4 14/15] printk: kmsg_dump: remove _nolock() variants John Ogness
2021-03-03 10:15 ` [PATCH next v4 15/15] printk: console: remove unnecessary safe buffer usage John Ogness
2021-03-03 13:18 ` lkml delivery: was: Re: [PATCH next v4 00/15] printk: remove logbuf_lock Petr Mladek
2021-03-03 14:34   ` Steven Rostedt
2021-03-03 15:34 ` Petr Mladek
2021-03-08 15:09   ` Petr Mladek

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