linux-kernel - Re: [PATCH] ASoC: soc-compress: Fix deadlock in soc_compr_open

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Date:   Thu, 15 Jun 2023 15:26:07 +0000
From:   Carlos Llamas <cmllamas@...gle.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     yixuanjiang <yixuanjiang@...gle.com>, vkoul@...nel.org,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] ASoC: soc-compress: Fix deadlock in soc_compr_open_fe

On Thu, Jun 15, 2023 at 01:56:35AM +0100, Mark Brown wrote:
> On Tue, Jun 13, 2023 at 02:23:50PM +0800, yixuanjiang wrote:
> > Modify the error handling flow by release lock.
> > The require pcm_mutex will keep holding if open fail.
> 
> > +++ b/sound/soc/soc-compress.c
> > @@ -166,6 +166,7 @@ static int soc_compr_open_fe(struct snd_compr_stream *cstream)
> >  	snd_soc_dai_compr_shutdown(cpu_dai, cstream, 1);
> >  out:
> >  	dpcm_path_put(&list);
> > +	mutex_unlock(&fe->card->pcm_mutex);
> >  be_err:
> 
> This is really hard to follow due to the lack of any mutex_lock()s in
> the function, I think because this is intended to undo
> snd_soc_dpcm_mutex_lock(fe) but if that's the case why is it not using
> snd_soc_dpcm_mutex_unlock(fe) like the success path does?  Given the use
> of classes not doing that looks like it'll create lockdep issues.
> 
> I'd expect the unlock to match the lock.

Yes, and judging from the context of the patch I believe this was based
off of stable 5.15.y tree. The locking has been refactored since. So
Yixuan, please rebase/adjust your patch on top of Linus's mainline tree
and resend. Thanks!

--
Carlos Llamas