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

Takashi Iwai wrote, on 22/10/14 00:08:

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@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@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);

Hi, I applied this patch, rebuilt the kernel and am running it now and have not seen the "pulseaudio possible recursive locking" message yet.

For the previous 4 reboots with earlier kernels 3.17.0+ / 3.18.0-rc1 I saw the "pulseaudio possible recursive locking" message appear about 5 minutes after boot-up.

Thanks for your help!

Arthur.