Commit 1b0fb5a5 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer

dm bufio: avoid a possible ABBA deadlock

__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.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 86331f39
...@@ -940,10 +940,11 @@ static void __get_memory_limit(struct dm_bufio_client *c, ...@@ -940,10 +940,11 @@ static void __get_memory_limit(struct dm_bufio_client *c,
{ {
unsigned long buffers; unsigned long buffers;
if (ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch) { if (unlikely(ACCESS_ONCE(dm_bufio_cache_size) != dm_bufio_cache_size_latch)) {
mutex_lock(&dm_bufio_clients_lock); if (mutex_trylock(&dm_bufio_clients_lock)) {
__cache_size_refresh(); __cache_size_refresh();
mutex_unlock(&dm_bufio_clients_lock); mutex_unlock(&dm_bufio_clients_lock);
}
} }
buffers = dm_bufio_cache_size_per_client >> buffers = dm_bufio_cache_size_per_client >>
......
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