This is a note to let you know that I've just added the patch titled
dm-delay: fix a race between delay_presuspend and delay_bio
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-delay-fix-a-race-between-delay_presuspend-and-del.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
commit 6d4ac18ce5263caf8368f49ae9dd0e171823015c
Author: Mikulas Patocka <[email protected]>
Date: Wed Nov 29 13:38:43 2023 -0500
dm-delay: fix a race between delay_presuspend and delay_bio
[ Upstream commit 6fc45b6ed921dc00dfb264dc08c7d67ee63d2656 ]
In delay_presuspend, we set the atomic variable may_delay and then stop
the timer and flush pending bios. The intention here is to prevent the
delay target from re-arming the timer again.
However, this test is racy. Suppose that one thread goes to delay_bio,
sees that dc->may_delay is one and proceeds; now, another thread executes
delay_presuspend, it sets dc->may_delay to zero, deletes the timer and
flushes pending bios. Then, the first thread continues and adds the bio to
delayed->list despite the fact that dc->may_delay is false.
Fix this bug by changing may_delay's type from atomic_t to bool and
only access it while holding the delayed_bios_lock mutex. Note that we
don't have to grab the mutex in delay_resume because there are no bios
in flight at this point.
Signed-off-by: Mikulas Patocka <[email protected]>
Cc: [email protected]
Signed-off-by: Mike Snitzer <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
diff --git a/drivers/md/dm-delay.c b/drivers/md/dm-delay.c
index f496213f8b675..7c0e7c662e07f 100644
--- a/drivers/md/dm-delay.c
+++ b/drivers/md/dm-delay.c
@@ -30,7 +30,7 @@ struct delay_c {
struct workqueue_struct *kdelayd_wq;
struct work_struct flush_expired_bios;
struct list_head delayed_bios;
- atomic_t may_delay;
+ bool may_delay;
struct delay_class read;
struct delay_class write;
@@ -191,7 +191,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int
argc, char **argv)
INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
INIT_LIST_HEAD(&dc->delayed_bios);
mutex_init(&dc->timer_lock);
- atomic_set(&dc->may_delay, 1);
+ dc->may_delay = true;
dc->argc = argc;
ret = delay_class_ctr(ti, &dc->read, argv);
@@ -245,7 +245,7 @@ static int delay_bio(struct delay_c *dc, struct delay_class
*c, struct bio *bio)
struct dm_delay_info *delayed;
unsigned long expires = 0;
- if (!c->delay || !atomic_read(&dc->may_delay))
+ if (!c->delay)
return DM_MAPIO_REMAPPED;
delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));
@@ -254,6 +254,10 @@ static int delay_bio(struct delay_c *dc, struct
delay_class *c, struct bio *bio)
delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay);
mutex_lock(&delayed_bios_lock);
+ if (unlikely(!dc->may_delay)) {
+ mutex_unlock(&delayed_bios_lock);
+ return DM_MAPIO_REMAPPED;
+ }
c->ops++;
list_add_tail(&delayed->list, &dc->delayed_bios);
mutex_unlock(&delayed_bios_lock);
@@ -267,7 +271,10 @@ static void delay_presuspend(struct dm_target *ti)
{
struct delay_c *dc = ti->private;
- atomic_set(&dc->may_delay, 0);
+ mutex_lock(&delayed_bios_lock);
+ dc->may_delay = false;
+ mutex_unlock(&delayed_bios_lock);
+
del_timer_sync(&dc->delay_timer);
flush_bios(flush_delayed_bios(dc, 1));
}
@@ -276,7 +283,7 @@ static void delay_resume(struct dm_target *ti)
{
struct delay_c *dc = ti->private;
- atomic_set(&dc->may_delay, 1);
+ dc->may_delay = true;
}
static int delay_map(struct dm_target *ti, struct bio *bio)
