Re: Re : Re: Sound+USB: deadlock problem

[Takashi Iwai]

At Wed, 14 Nov 2012 11:44:44 +0100,
Matthieu CASTET wrote:
> 
> A deadlock was detected with this patch. You need the following patch [1]

I'm going to send a pull request including this fix commit to Linus
tomorrow.


Takashi

> 
> 
> Matthieu
> 
> 
> > 3.2-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Takashi Iwai <tiwai@xxxxxxx>
> > 
> > commit 34f3c89fda4fba9fe689db22253ca8db2f5e6386 upstream.
> > 
> > Replace mutex with rwsem for codec->shutdown protection so that
> > concurrent accesses are allowed.
> > 
> > Also add the protection to snd_usb_autosuspend() and
> > snd_usb_autoresume(), too.
> > 
> > Reported-by: Matthieu CASTET <matthieu.castet@xxxxxxxxxx>
> > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> > ---
> >  sound/usb/card.c     | 12 ++++++++----
> >  sound/usb/mixer.c    | 12 ++++++------
> >  sound/usb/pcm.c      | 12 ++++++------
> >  sound/usb/usbaudio.h |  2 +-
> >  4 files changed, 21 insertions(+), 17 deletions(-)
> 
> 
> 
> [1]
> 
> Takashi Iwai a Ãcrit :
> > At Tue, 13 Nov 2012 10:39:14 +0100,
> > Jiri Slaby wrote:
> >> On 11/13/2012 09:45 AM, Takashi Iwai wrote:
> >>> At Tue, 13 Nov 2012 09:30:10 +0100,
> >>> Jiri Slaby wrote:
> >>>> On 11/13/2012 09:28 AM, Takashi Iwai wrote:
> >>>>> At Tue, 13 Nov 2012 09:26:17 +0100,
> >>>>> Jiri Slaby wrote:
> >>>>>> Hello,
> >>>>>>
> >>>>>> I've just plugged+unplugged+plugged my USB audio card and the audio
> >>>>>> subsystem got stuck:
> >>>>> Which kernel?  If it's older than 3.7-rc5, could you try 3.7-rc5?
> >>>> Oh, forgot to mention:
> >>>> 3.7.0-rc5-next-20121112_64+
> >>> Through a quick glance, one of mutex locks seems stuck.
> >>> Just a blind short -- does the patch below cure the problem?
> >> Yes, this helps.
> >>
> >> Adding a LOCKDEP splash _before_ applying the patch:
> > 
> > Thanks, this helps much for understanding the cause.
> > It's a new rwsem in the usb-audio driver that deadlocks.
> > 
> > Although the previous patch fixes the deadlock it opens the race
> > again. 
> > 
> > Could you try the patch below instead?  The rwsem above doesn't have
> > to be taken for the whole operation, but just needs to protect for
> > turning on the flag.  The patch below should suffice for protecting
> > races but avoids the deadlock.
> > 
> > 
> > Takashi
> > 
> > ---
> > diff --git a/sound/usb/card.c b/sound/usb/card.c
> > index 282f0fc..dbf7999 100644
> > --- a/sound/usb/card.c
> > +++ b/sound/usb/card.c
> > @@ -559,9 +559,11 @@ static void snd_usb_audio_disconnect(struct usb_device *dev,
> >  		return;
> >  
> >  	card = chip->card;
> > -	mutex_lock(&register_mutex);
> >  	down_write(&chip->shutdown_rwsem);
> >  	chip->shutdown = 1;
> > +	up_write(&chip->shutdown_rwsem);
> > +
> > +	mutex_lock(&register_mutex);
> >  	chip->num_interfaces--;
> >  	if (chip->num_interfaces <= 0) {
> >  		snd_card_disconnect(card);
> > @@ -582,11 +584,9 @@ static void snd_usb_audio_disconnect(struct usb_device *dev,
> >  			snd_usb_mixer_disconnect(p);
> >  		}
> >  		usb_chip[chip->index] = NULL;
> > -		up_write(&chip->shutdown_rwsem);
> >  		mutex_unlock(&register_mutex);
> >  		snd_card_free_when_closed(card);
> >  	} else {
> > -		up_write(&chip->shutdown_rwsem);
> >  		mutex_unlock(&register_mutex);
> >  	}
> >  }
> > --
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> > 
> 
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