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Subject: Re: [PATCH] ASoC: davinci-mcasp: Fix dma_chan refcnt leak when
 getting dma type
To:     Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, <alsa-devel@alsa-project.org>,
        <linux-kernel@vger.kernel.org>
CC:     <yuanxzhang@fudan.edu.cn>, <kjlu@umn.edu>,
        Xin Tan <tanxin.ctf@gmail.com>
References: <1587818916-38730-1-git-send-email-xiyuyang19@fudan.edu.cn>
From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
Message-ID: <a64cfa62-c377-b516-7386-23340e532285@ti.com>
Date:   Tue, 28 Apr 2020 11:13:15 +0300
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On 25/04/2020 15.48, Xiyu Yang wrote:
> davinci_mcasp_get_dma_type() invokes dma_request_chan(), which returns a
> reference of the specified dma_chan object to "chan" with increased
> refcnt.
> 
> When davinci_mcasp_get_dma_type() returns, local variable "chan" becomes
> invalid, so the refcount should be decreased to keep refcount balanced.
> 
> The reference counting issue happens in one exception handling path of
> davinci_mcasp_get_dma_type(). When chan device is NULL, the function
> forgets to decrease the refcnt increased by dma_request_chan(), causing
> a refcnt leak.
> 
> Fix this issue by calling dma_release_channel() when chan device is
> NULL.
> 
> Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
> ---
>  sound/soc/ti/davinci-mcasp.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/soc/ti/davinci-mcasp.c b/sound/soc/ti/davinci-mcasp.c
> index 734ffe925c4d..7a7db743dc5b 100644
> --- a/sound/soc/ti/davinci-mcasp.c
> +++ b/sound/soc/ti/davinci-mcasp.c
> @@ -1896,8 +1896,10 @@ static int davinci_mcasp_get_dma_type(struct davinci_mcasp *mcasp)
>  				PTR_ERR(chan));
>  		return PTR_ERR(chan);
>  	}
> -	if (WARN_ON(!chan->device || !chan->device->dev))
> +	if (WARN_ON(!chan->device || !chan->device->dev)) {
> +		dma_release_channel(chan);
>  		return -EINVAL;
> +	}

If we get a channel then chan->device and chan->device->dev never NULL,
it can not be.
I think the reason why this is here is that static checkers tends to
scream at us.

Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>

>  
>  	if (chan->device->dev->of_node)
>  		ret = of_property_read_string(chan->device->dev->of_node,
> 

- Péter

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