dm bufio: avoid a possible ABBA deadlock

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commit 1b0fb5a5b2 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@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Mikulas Patocka 2017-04-30 17:33:26 -04:00 • committed by Greg Kroah-Hartman

parent c5066c4c1b

commit 98e7b9d45b

1 changed files with 5 additions and 4 deletions

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drivers/md/dm-bufio.c

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