linux-kernel - Re: [BUG] sound: pci: trident: a possible data race

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Message-ID: <e334c065-5768-7710-bd70-059f7316157b@gmail.com>
Date:   Thu, 4 Oct 2018 11:08:45 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     keescook@...omium.org, perex@...ex.cz, alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] sound: pci: trident: a possible data race

Thanks for the reply :)


On 2018/10/3 23:54, Takashi Iwai wrote:
> On Wed, 03 Oct 2018 14:50:25 +0200,
> Jia-Ju Bai wrote:
>> CPU0:
>> snd_trident_hw_free
>>      snd_trident_free_voice
>>              line 3870: spin_lock_irqsave()
>>              line 3881: voice->substream = NULL; [WRITE]
>> CPU1:
>> snd_trident_interrupt
>>      line 3798: snd_pcm_period_elapsed(voice->substream);  [READ]
>>
>> As for voice->substream, the WRITE operation in CPU0 is performed
>> with holding a spinlock, but the READ operation in CPU1 is performed
>> without holding this spinlock, so there may exist a data race.
> Thanks for the report.
>
> The actual crash must be very unlikely, almost 0%, though.
> snd_trident_hw_free() is called always after the PCM stream gets
> stopped via trigger callback, i.e. at the moment, there is no
> corresponding interrupt is generated for that voice entry.

How about the case that playback and capture are performed concurrently?
Namely, snd_trident_hw_free() is called for playback, and the interrupt 
is generated for capture.

> And the hardware is very old, I bet only a handful people still using
> in the whole world :)

I have this hardware, so I am the one of these handful people ;)


Best wishes,
Jia-Ju Bai