5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mikulas Patocka mpatocka@redhat.com
[ 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 mpatocka@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer snitzer@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm-delay.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
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)