Commit 6fc45b6e authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

dm-delay: fix a race between delay_presuspend and delay_bio 



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: default avatarMikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
parent b85ea95d

drivers/md/dm-delay.c

+11 −5
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ struct delay_c { 
	struct work_struct flush_expired_bios;

	struct list_head delayed_bios;

	struct task_struct *worker;

	atomic_t may_delay;

	bool may_delay;



	struct delay_class read;

	struct delay_class write;
@@ -236,7 +236,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv) 


	ti->private = dc;

	INIT_LIST_HEAD(&dc->delayed_bios);

	atomic_set(&dc->may_delay, 1);

	dc->may_delay = true;

	dc->argc = argc;



	ret = delay_class_ctr(ti, &dc->read, argv);
@@ -312,7 +312,7 @@ 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));
@@ -321,6 +321,10 @@ 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);
@@ -337,7 +341,9 @@ 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);



	if (delay_is_fast(dc))

		flush_delayed_bios_fast(dc, true);
@@ -351,7 +357,7 @@ 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)