The function __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 the function cleanup_old_buffers dm_bufio_clients_lock is taken before the client lock.
This results in a possible deadlock and lockdep engine warning. This patch fixes the 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 be allocated. The patch also adds "unlikely" to the if confition, so that the optimizer assumes that the condition is false. Signed-off-by: Mikulas Patocka <[email protected]> Cc: [email protected] --- drivers/md/dm-bufio.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) Index: linux-2.6/drivers/md/dm-bufio.c =================================================================== --- linux-2.6.orig/drivers/md/dm-bufio.c +++ linux-2.6/drivers/md/dm-bufio.c @@ -959,10 +959,11 @@ 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 >> -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
