This is a note to let you know that I've just added the patch titled dm bufio: avoid a possible ABBA deadlock to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: dm-bufio-avoid-a-possible-abba-deadlock.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37 Mon Sep 17 00:00:00 2001 From: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Sun, 30 Apr 2017 17:33:26 -0400 Subject: dm bufio: avoid a possible ABBA deadlock From: Mikulas Patocka <mpatocka@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -923,10 +923,11 @@ 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 >> Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are queue-4.9/dm-bufio-avoid-a-possible-abba-deadlock.patch queue-4.9/dm-cache-metadata-fail-operations-if-fail_io-mode-has-been-established.patch queue-4.9/dm-raid-select-the-kconfig-option-config_md_raid0.patch queue-4.9/dm-bufio-make-the-parameter-retain_bytes-unsigned-long.patch queue-4.9/dm-bufio-check-new-buffer-allocation-watermark-every-30-seconds.patch