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