[alsa-devel] 3.18.0-rc1 pulseaudio possible recursive locking

[Takashi Iwai]

At Tue, 21 Oct 2014 07:27:34 +0200,
Takashi Iwai wrote:
> 
> At Tue, 21 Oct 2014 00:30:59 +1030,
> Arthur Marsh wrote:
> > 
> > Hi, I have been seeing this a few times lately, and noticed that it was 
> > still present
> > 
> > Is this the right place to report it or should I be reporting a bug 
> > against pulseaudio?
> 
> This is likely a false-positive report, so ignore it unless you really
> encounter the deadlock by this.

Or try the patch below.  This seems hitting more often, so it's maybe
worth to put into 3.18-rc2.  Let me know if this solves the problem.


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: pcm: Fix false lockdep warnings

As PCM core handles the multiple linked streams in parallel, lockdep
gets confused (partly because of weak annotations) and spews the
false-positive warnings.  This hasn't been a problem for long time but
the latest PCM lock path update seems to have woken up a sleeping
dog.

Here is an attempt to paper over this issue: pass the lock subclass
just calculated from the depth in snd_pcm_action_group().  Also, a
(possibly) wrong lock subclass set in snd_pcm_action_lock_mutex() is
dropped, too.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/pcm_native.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 815396d8427f..166d59cdc86b 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -781,16 +781,15 @@ static int snd_pcm_action_group(struct action_ops *ops,
 {
 	struct snd_pcm_substream *s = NULL;
 	struct snd_pcm_substream *s1;
-	int res = 0;
+	int res = 0, depth = 1;
 
 	snd_pcm_group_for_each_entry(s, substream) {
 		if (do_lock && s != substream) {
 			if (s->pcm->nonatomic)
-				mutex_lock_nested(&s->self_group.mutex,
-						  SINGLE_DEPTH_NESTING);
+				mutex_lock_nested(&s->self_group.mutex, depth);
 			else
-				spin_lock_nested(&s->self_group.lock,
-						 SINGLE_DEPTH_NESTING);
+				spin_lock_nested(&s->self_group.lock, depth);
+			depth++;
 		}
 		res = ops->pre_action(s, state);
 		if (res < 0)
@@ -906,8 +905,7 @@ static int snd_pcm_action_lock_mutex(struct action_ops *ops,
 	down_read(&snd_pcm_link_rwsem);
 	if (snd_pcm_stream_linked(substream)) {
 		mutex_lock(&substream->group->mutex);
-		mutex_lock_nested(&substream->self_group.mutex,
-				  SINGLE_DEPTH_NESTING);
+		mutex_lock(&substream->self_group.mutex);
 		res = snd_pcm_action_group(ops, substream, state, 1);
 		mutex_unlock(&substream->self_group.mutex);
 		mutex_unlock(&substream->group->mutex);
-- 
2.1.2