linux-kernel - Re: [BUG] ALSA: core: pcm_memory: a possible data race in do_alloc

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Message-ID: <4d0931bf-b356-6969-5aaf-b663d7f2b21a@perex.cz>
Date:   Mon, 26 Jun 2023 09:56:47 +0200
From:   Jaroslav Kysela <perex@...ex.cz>
To:     Takashi Iwai <tiwai@...e.de>, Tuo Li <islituo@...il.com>
Cc:     tiwai@...e.com, alsa-devel@...a-project.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        baijiaju1990@...look.com
Subject: Re: [BUG] ALSA: core: pcm_memory: a possible data race in
 do_alloc_pages()

On 26. 06. 23 9:33, Takashi Iwai wrote:
> On Mon, 26 Jun 2023 09:31:18 +0200,
> Tuo Li wrote:
>>
>>
>> Hello,
>>
>> Thank you for your reply!
> 
> FWIW, the simplest fix would be something like below, just extending
> the mutex coverage.  But it'll serialize the all calls, so it might
> influence on the performance, while it's the safest way.

It may be better to update total_pcm_alloc_bytes before 
snd_dma_alloc_dir_pages() call and decrease this value when allocation fails 
to allow parallel allocations. Then the mutex can be held only for the 
total_pcm_alloc_bytes variable update.

Eventually, total_pcm_alloc_bytes may be atomic.

					Jaroslav

-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.