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| author |   Mikulas Patocka <mpatocka@redhat.com> | 2017-04-30 17:33:26 -0400 |
|---|---|---|
| committer |   Mike Snitzer <snitzer@redhat.com> | 2017-05-01 15:18:13 -0400 |
| commit | 1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37 (patch) | |
| tree | 7db34655122c059ee824083e4a682e229be2adc7 /drivers/md/dm-bufio.c | |
| parent | dm mpath: make it easier to detect unintended I/O request flushes (diff) | |
| download | linux-dev-1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37.tar.xz linux-dev-1b0fb5a5b2dc0dddcfa575060441a7176ba7ac37.zip | |
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: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md/dm-bufio.c')
| -rw-r--r-- | drivers/md/dm-bufio.c | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index 280b56c229d6..fd28146dd952 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -940,10 +940,11 @@ static void __get_memory_limit(struct dm_bufio_client *c, { 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 >> |