When thin-volume was built on loop device, if available memory is low, the following deadlock can be triggered. One process P1 was allocating memory with GFP_FS flag, direct alloc fail, memory reclaim invoked memory shrinker in dm_bufio, dm_bufio_shrink_scan() run, mutex dm_bufio_client->lock was acquired, then P1 wait for dm_buffer io done in __try_evict_buffer->()__try_evict_buffer(). But this io may never done as it was issued to the underlying loop device who forward it using fs direct-io, there some memory allocation were using GFP_FS(like do_blockdev_direct_IO()), if direct alloc fail, memory reclaim will invoke memory shrinker in dm_bufio, where dm_bufio_shrink_scan() will be invoked, since the mutex was already hold by P1, the loop thread will hung, io will never done. ABBA deadlock. Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx> --- Changes in v2: - refine the commit log drivers/md/dm-bufio.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index 2a48ea3f1b30..b6b5acc92ca2 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -1599,9 +1599,7 @@ dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) 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); -- 2.17.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
