linux-kernel - Re: [PATCH 2/5] ASoC: dwc: Don't allow negative use counts

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Message-ID: <20141204105121.GQ7712@sirena.org.uk>
Date:	Thu, 4 Dec 2014 10:51:21 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Andrew Jackson <Andrew.Jackson@....com>
Cc:	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rajeev Kumar <rajeevkumar.linux@...il.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Liviu Dudau <Liviu.Dudau@....com>
Subject: Re: [PATCH 2/5] ASoC: dwc: Don't allow negative use counts

On Thu, Dec 04, 2014 at 09:00:35AM +0000, Andrew Jackson wrote:
> On 12/03/14 17:25, Mark Brown wrote:
> > On Wed, Dec 03, 2014 at 04:38:55PM +0000, Andrew Jackson wrote:

> >>  	case SNDRV_PCM_TRIGGER_STOP:
> >>  	case SNDRV_PCM_TRIGGER_SUSPEND:
> >>  	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
> >> -		dev->active--;
> >> +		if (dev->active > 0)
> >> +			dev->active--;

> > How is this triggering - this sounds like you're papering over some
> > other bug somewhere?

> When I looked at the code paths I couldn't convince myself that STOP
> wouldn't be called more than once.  Then actuve would be negative and
> the device might not be restartable.  I didn't have a problem per se,
> it was just that it seemed to be something of a loophole.

If you're just adding the check on the off chance that it might fire you
need to add a warning message as well - what your change does is make
the code look like it's supposed to have broken reference counting since
it has a check to silently fix up and ignore problems.

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