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ALSA: seq: Fix nested rwsem annotation for lockdep splat

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commit 1f20f9ff57ca23b9f5502fca85ce3977e8496cb1 upstream.

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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Takashi Iwai 2017-10-29 11:10:43 +01:00 committed by syphyr
parent 6c935b70b7
commit f3f573d4aa
1 changed files with 1 additions and 1 deletions
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2
sound/core/seq/seq_clientmgr.c
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@ -676,7 +676,7 @@ static int deliver_to_subscribers(struct snd_seq_client *client,
if (atomic)
read_lock(&grp->list_lock);
else
down_read(&grp->list_mutex);
down_read_nested(&grp->list_mutex, hop);
list_for_each_entry(subs, &grp->list_head, src_list) {
/* both ports ready? */
if (atomic_read(&subs->ref_count) != 2)