linux-kernel - Re: [BUG] sound/soc/samsung: a possible sleep-in-atomic bugs in s3c_pcm_hw

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Date:   Thu, 14 Dec 2017 11:11:07 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Jia-Ju Bai <baijiaju1990@....com>
Cc:     sbkim73@...sung.com, Sylwester Nawrocki <s.nawrocki@...sung.com>,
        lgirdwood@...il.com, broonie@...nel.org, perex@...ex.cz,
        tiwai@...e.com, alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] sound/soc/samsung: a possible sleep-in-atomic bugs in s3c_pcm_hw_params

On Tue, Dec 12, 2017 at 2:24 AM, Jia-Ju Bai <baijiaju1990@....com> wrote:
> According to sound/soc/samsung/pcm.c, the kernel module may sleep under a
> spinlock.
> The function call path is:
> s3c_pcm_hw_params (acquire the spinlock)
>   clk_get_rate
>     clk_core_get_rate
>       clk_prepare_lock
>         mutex_lock --> may sleep
>
> I do not find a good way to fix it, so I only report.
> This possible bug is found by my static analysis tool (DSAC) and my code
> review.

Thanks for the report. Your finding looks correct, the code might
sleep under spinlock.

I do not see easy solution. Maybe the readl(regs + S3C_PCM_CLKCTL) and
clk_get_rate() could be moved before spinlock. The second path
modifying it - s3c_pcm_set_sysclk() - is not protected by it. The
spinlock is not effective around it.

Best regards,
Krzysztof