2022-05-24 06:27:58

by Duoming Zhou

Subject: [PATCH] mtd: Fix deadlock caused by cancel_work_sync in sm_release

There is a deadlock between sm_release and sm_cache_flush_work
which is a work item. The cancel_work_sync in sm_release will
not return until sm_cache_flush_work is finished. If we hold
mutex_lock and use cancel_work_sync to wait the work item to
finish, the work item also requires mutex_lock. As a result,
the sm_release will be blocked forever. The race condition is
shown below:

(Thread 1) | (Thread 2)
sm_release |
mutex_lock(&ftl->mutex) | sm_cache_flush_work
| mutex_lock(&ftl->mutex)
cancel_work_sync | ...

This patch moves del_timer_sync and cancel_work_sync out of
mutex_lock in order to mitigate deadlock.

Fixes: 7d17c02a01a1 ("mtd: Add new SmartMedia/xD FTL")
Signed-off-by: Duoming Zhou <[email protected]>
---
drivers/mtd/sm_ftl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/sm_ftl.c b/drivers/mtd/sm_ftl.c
index 0cff2cda1b5..7f955fade83 100644
--- a/drivers/mtd/sm_ftl.c
+++ b/drivers/mtd/sm_ftl.c
@@ -1111,9 +1111,9 @@ static void sm_release(struct mtd_blktrans_dev *dev)
{
struct sm_ftl *ftl = dev->priv;

- mutex_lock(&ftl->mutex);
del_timer_sync(&ftl->timer);
cancel_work_sync(&ftl->flush_work);
+ mutex_lock(&ftl->mutex);
sm_cache_flush(ftl);
mutex_unlock(&ftl->mutex);
}
--
2.17.1

2022-06-09 12:58:32

by Miquel Raynal

Subject: Re: [PATCH] mtd: Fix deadlock caused by cancel_work_sync in sm_release

On Tue, 2022-05-24 at 04:48:41 UTC, Duoming Zhou wrote:
> There is a deadlock between sm_release and sm_cache_flush_work
> which is a work item. The cancel_work_sync in sm_release will
> not return until sm_cache_flush_work is finished. If we hold
> mutex_lock and use cancel_work_sync to wait the work item to
> finish, the work item also requires mutex_lock. As a result,
> the sm_release will be blocked forever. The race condition is
> shown below:
>
> (Thread 1) | (Thread 2)
> sm_release |
> mutex_lock(&ftl->mutex) | sm_cache_flush_work
> | mutex_lock(&ftl->mutex)
> cancel_work_sync | ...
>
> This patch moves del_timer_sync and cancel_work_sync out of
> mutex_lock in order to mitigate deadlock.
>
> Fixes: 7d17c02a01a1 ("mtd: Add new SmartMedia/xD FTL")
> Signed-off-by: Duoming Zhou <[email protected]>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel