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Date:   Tue, 27 Jun 2023 12:01:29 +0200
Message-ID: <87jzvpfcli.wl-tiwai@suse.de>
From:   Takashi Iwai <tiwai@suse.de>
To:     Chengfeng Ye <dg573847474@gmail.com>
Cc:     perex@perex.cz, tiwai@suse.com, alsa-devel@alsa-project.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ALSA: sb: fix potential deadlock on &chip->mixer_lock
In-Reply-To: <20230627095616.5333-1-dg573847474@gmail.com>
References: <20230627095616.5333-1-dg573847474@gmail.com>
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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@gmail.com>

I believe it's a false-positive.  There is already a call
	spin_lock_irqsave(&chip->reg_lock, flags);
beforehand.


thanks,

Takashi