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Message-Id: <20170523200858.382600912@linuxfoundation.org>
Date: Tue, 23 May 2017 22:08:38 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Mikulas Patocka <mpatocka@...hat.com>,
Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.4 012/103] dm bufio: avoid a possible ABBA deadlock
4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Mikulas Patocka <mpatocka@...hat.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@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -914,10 +914,11 @@ 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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