linux-kernel - Re: [PATCH] ALSA: aloop: Fix &cable->lock deadlock issues

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Date:   Sun, 25 Jun 2023 20:14:22 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     YE Chengfeng <cyeaa@...nect.ust.hk>
Cc:     "perex@...ex.cz" <perex@...ex.cz>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "pteerapong@...omium.org" <pteerapong@...omium.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: aloop: Fix &cable->lock deadlock issues

On Sun, 25 Jun 2023 18:22:56 +0200,
YE Chengfeng wrote:
> 
> The timer loopback_jiffies_timer_function is executed under
> bottom-half softirq context and require a spinlock, thus
> other process context code requiring the same lock (i.e.,
> loopback_trigger, loopback_pointer) can deadlock with the
> timer if it is preempted while holding the lock.
> 
> Deadlock scenario:
> loopback_trigger
>     -> spin_lock(&cable->lock);
>         <timer interrupt>
>         -> loopback_jiffies_timer_function
>         -> spin_lock_irqsave(&dpcm->cable->lock, flags);
> 
> Fix the potential deadlock by using spin_lock_irqsave.

Similarly like the patch for snd-dummy, this change looks superfluous,
too.


thanks,

Takashi