[dm-devel] [PATCH v2] dm-bufio: fix deadlock with loop device
Junxiao Bi
junxiao.bi at oracle.com
Wed Jul 10 00:17:19 UTC 2019
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 at oracle.com>
---
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
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