| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.11 025/197] dm bufio: avoid a possible ABBA deadlock | Date | Tue, 23 May 2017 22:06:26 +0200 |
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4.11-stable review patch. If anyone has any objections, please let me know.
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From: Mikulas Patocka <mpatocka@redhat.com>
commit 1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37 upstream.
__get_memory_limit() tests if dm_bufio_cache_size changed and calls __cache_size_refresh() if it did. It takes dm_bufio_clients_lock while it already holds the client lock. However, lock ordering is violated because in cleanup_old_buffers() dm_bufio_clients_lock is taken before the client lock.
This results in a possible deadlock and lockdep engine warning.
Fix this deadlock by changing mutex_lock() to mutex_trylock(). If the lock can't be taken, it will be re-checked next time when a new buffer is allocated.
Also add "unlikely" to the if condition, so that the optimizer assumes that the condition is false.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/md/dm-bufio.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
--- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -933,10 +933,11 @@ static void __get_memory_limit(struct dm { unsigned long buffers; - if (ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch) { - mutex_lock(&dm_bufio_clients_lock); - __cache_size_refresh(); - mutex_unlock(&dm_bufio_clients_lock); + if (unlikely(ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch)) { + if (mutex_trylock(&dm_bufio_clients_lock)) { + __cache_size_refresh(); + mutex_unlock(&dm_bufio_clients_lock); + } } buffers = dm_bufio_cache_size_per_client >>
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