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Message-Id: <20190724191718.479146711@linuxfoundation.org>
Date: Wed, 24 Jul 2019 21:22:20 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Junxiao Bi <junxiao.bi@...cle.com>,
Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.19 271/271] dm bufio: fix deadlock with loop device
From: Junxiao Bi <junxiao.bi@...cle.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@...r.kernel.org
Signed-off-by: Junxiao Bi <junxiao.bi@...cle.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -1602,9 +1602,7 @@ 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);
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