From mboxrd@z Thu Jan 1 00:00:00 1970 From: Junxiao Bi Subject: [PATCH v2] dm-bufio: fix deadlock with loop device Date: Tue, 9 Jul 2019 17:17:19 -0700 Message-ID: <20190710001719.2504-1-junxiao.bi@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: dm-devel@redhat.com Cc: honglei.wang@oracle.com, mpatocka@redhat.com, agk@redhat.com, snitzer@redhat.com, junxiao.bi@oracle.com List-Id: dm-devel.ids 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 --- 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