diff options
| author | Takashi Iwai <tiwai@suse.de> | 2016-02-03 08:32:44 +0100 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2016-02-03 14:51:51 +0100 |
| commit | 7f0973e973cd74aa40747c9d38844560cd184ee8 (patch) | |
| tree | 995f82e9dfe6c69c8c6136f61be99577de81a85b /sound/core/seq/seq_clientmgr.c | |
| parent | 81f577542af15640cbcb6ef68baa4caa610cbbfc (diff) | |
ALSA: seq: Fix lockdep warnings due to double mutex locks
The port subscription code uses double mutex locks for source and
destination ports, and this may become racy once when wrongly set up.
It leads to lockdep warning splat, typically triggered by fuzzer like
syzkaller, although the actual deadlock hasn't been seen, so far.
This patch simplifies the handling by reducing to two single locks, so
that no lockdep warning will be trigger any longer.
By splitting to two actions, a still-in-progress element shall be
added in one list while handling another. For ignoring this element,
a new check is added in deliver_to_subscribers().
Along with it, the code to add/remove the subscribers list element was
cleaned up and refactored.
BugLink: http://lkml.kernel.org/r/CACT4Y+aKQXV7xkBW9hpQbzaDO7LrUvohxWh-UwMxXjDy-yBD=A@mail.gmail.com
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core/seq/seq_clientmgr.c')
| -rw-r--r-- | sound/core/seq/seq_clientmgr.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c index 13cfa815732d..58e79e02f217 100644 --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -678,6 +678,9 @@ static int deliver_to_subscribers(struct snd_seq_client *client, else down_read(&grp->list_mutex); list_for_each_entry(subs, &grp->list_head, src_list) { + /* both ports ready? */ + if (atomic_read(&subs->ref_count) != 2) + continue; event->dest = subs->info.dest; if (subs->info.flags & SNDRV_SEQ_PORT_SUBS_TIMESTAMP) /* convert time according to flag with subscription */ |