From: Junxiao Bi junxiao.bi@oracle.com
commit bd293d071ffe65e645b4d8104f9d8fe15ea13862 upstream.
When thin-volume is built on loop device, if available memory is low, the following deadlock can be triggered:
One process P1 allocates memory with GFP_FS flag, direct alloc fails, memory reclaim invokes memory shrinker in dm_bufio, dm_bufio_shrink_scan() runs, mutex dm_bufio_client->lock is acquired, then P1 waits for dm_buffer IO to complete in __try_evict_buffer().
But this IO may never complete if issued to an underlying loop device that forwards it using direct-IO, which allocates memory using GFP_KERNEL (see: do_blockdev_direct_IO()). If allocation fails, memory reclaim will invoke memory shrinker in dm_bufio, dm_bufio_shrink_scan() will be invoked, and since the mutex is already held by P1 the loop thread will hang, and IO will never complete. Resulting in ABBA deadlock.
Cc: stable@vger.kernel.org Signed-off-by: Junxiao Bi junxiao.bi@oracle.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/md/dm-bufio.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -1585,9 +1585,7 @@ dm_bufio_shrink_scan(struct shrinker *sh unsigned long freed;
c = container_of(shrink, struct dm_bufio_client, shrinker); - if (sc->gfp_mask & __GFP_FS) - dm_bufio_lock(c); - else if (!dm_bufio_trylock(c)) + if (!dm_bufio_trylock(c)) return SHRINK_STOP;
freed = __scan(c, sc->nr_to_scan, sc->gfp_mask);