linux-kernel - Re: [PATCH] ALSA: sb: fix potential deadlock on &chip->mixer

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Date:   Tue, 27 Jun 2023 18:55:19 +0800
From:   叶澄锋 <dg573847474@...il.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: sb: fix potential deadlock on &chip->mixer_lock

Oh yes, sorry for not considering that one.

Best regards
Chengfeng

Takashi Iwai <tiwai@...e.de> 于2023年6月27日周二 18:01写道：
>
> On Tue, 27 Jun 2023 11:56:16 +0200,
> Chengfeng Ye wrote:
> >
> > As &chip->mixer_lock is also acquired by the irq snd_sb8dsp_interrupt()
> > which executes under hard-irq context, code executing under process
> > context should disable irq before acquiring the lock, otherwise
> > deadlock could happen if the process context hold the lock then
> > preempt by the interruption.
> >
> > As the ALSA Driver document described, PCM prepare callbacks are not
> > executed with irq disabled by default, thus the acquiring of
> > &chip->mixer_lock should be irq disabled.
> >
> > Possible deadlock scenario:
> > snd_sb8_playback_prepare
> >     -> spin_lock(&chip->mixer_lock);
> >         <irq interrupt>
> >         -> snd_sb8dsp_interrupt()
> >         -> snd_sb8_capture_trigger()
> >         -> spin_lock(&chip->mixer_lock); (deadlock here)
> >
> > This flaw was found using an experimental static analysis tool we are
> > developing for irq-related deadlock.
> >
> > The tentative patch fix the potential deadlock by spin_lock_irqsave().
> >
> > Signed-off-by: Chengfeng Ye <dg573847474@...il.com>
>
> I believe it's a false-positive.  There is already a call
>         spin_lock_irqsave(&chip->reg_lock, flags);
> beforehand.
>
>
> thanks,
>
> Takashi