[lkml]   [2019]   [Aug]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 4.4 085/158] dm bufio: fix deadlock with loop device
From: Junxiao Bi <>

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

Signed-off-by: Junxiao Bi <>
Signed-off-by: Mike Snitzer <>
Signed-off-by: Greg Kroah-Hartman <>

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
@@ -1561,9 +1561,7 @@ 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))

freed = __scan(c, sc->nr_to_scan, sc->gfp_mask);

 \ /
  Last update: 2019-08-02 11:39    [W:0.510 / U:0.416 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site