commit 1f20f9ff57ca23b9f5502fca85ce3977e8496cb1
author Takashi Iwai <tiwai@suse.de> Sun Oct 29 11:10:43 2017 +0100
committer Takashi Iwai <tiwai@suse.de> Tue Oct 31 09:09:10 2017 +0100
tree 51212012496d31592812a4bfafb4f782d3840e7e
parent 79fb0518fec8c8b4ea7f1729f54f293724b3dbb0

ALSA: seq: Fix nested rwsem annotation for lockdep splat

syzkaller reported the lockdep splat due to the possible deadlock of
grp->list_mutex of each sequencer client object.  Actually this is
rather a false-positive report due to the missing nested lock
annotations.  The sequencer client may deliver the event directly to
another client which takes another own lock.

For addressing this issue, this patch replaces the simple down_read()
with down_read_nested().  As a lock subclass, the already existing
"hop" can be re-used, which indicates the depth of the call.

Reference: http://lkml.kernel.org/r/089e082686ac9b482e055c832617@google.com
Reported-by: syzbot <bot+7feb8de6b4d6bf810cf098bef942cc387e79d0ad@syzkaller.appspotmail.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>