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

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Date:   Tue, 27 Jun 2023 12:01:29 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Chengfeng Ye <dg573847474@...il.com>
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

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