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

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Message-ID: <3be565e2-d2fe-689b-52a9-f6bed0e215f1@gmail.com>
Date:   Thu, 4 Oct 2018 17:17:52 +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



On 2018/10/4 13:24, Takashi Iwai wrote:
> On Thu, 04 Oct 2018 05:08:45 +0200,
> Jia-Ju Bai wrote:
>> 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.
> They are different substreams, hence it won't pick up the substream
> object.

Actually, I performed a runtime testing, and found that 
snd_trident_hw_free() and snd_trident_interrupt() are executed concurrently.
However, I did not check the substream object, so I guess this report 
was produced in the case that I mentioned.
Anyway, my report should be false, sorry...


Best wishes,
Jia-Ju Bai