linux-kernel - Re: [PATCH v2 1/3] dmaengine: imx-sdma: fix buffer ownership

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Message-ID: <7d694da8ffe098c6c8f6fe9c3a2306fda55eb655.camel@pengutronix.de>
Date:   Thu, 19 Sep 2019 12:27:58 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Philipp Puschmann <philipp.puschmann@...ix.com>,
        linux-kernel@...r.kernel.org
Cc:     yibin.gong@....com, fugang.duan@....com, dan.j.williams@...el.com,
        vkoul@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] dmaengine: imx-sdma: fix buffer ownership

Hi Philipp,

On Do, 2019-09-19 at 12:23 +0200, Philipp Puschmann wrote:
> BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the
> buffer, when 0 ARM owns it. When processing the buffers in
> sdma_update_channel_loop the ownership of the currently processed
> buffer was set to SDMA again before running the callback function of
> the buffer and while the sdma script may be running in parallel. So
> there was the possibility to get the buffer overwritten by SDMA
> before
> it has been processed by kernel leading to kind of random errors in
> the
> upper layers, e.g. bluetooth.
> 
> Signed-off-by: Philipp Puschmann <philipp.puschmann@...ix.com>
> 
> ---
> 
> Changelog v2:
>  - add dma_wb()
> 
>  drivers/dma/imx-sdma.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 9ba74ab7e912..e029a2443cfc 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct
> sdma_channel *sdmac)
>  		*/
>  
>  		desc->chn_real_count = bd->mode.count;
> -		bd->mode.status |= BD_DONE;
>  		bd->mode.count = desc->period_len;
>  		desc->buf_ptail = desc->buf_tail;
>  		desc->buf_tail = (desc->buf_tail + 1) % desc->num_bd;
> @@ -817,6 +816,9 @@ static void sdma_update_channel_loop(struct
> sdma_channel *sdmac)
>  		dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL);
>  		spin_lock(&sdmac->vc.lock);
>  
> +		dma_wb();

Has this change been tested? The function you want here is called
dma_wmb().

Regards,
Lucas

> +		bd->mode.status |= BD_DONE;
> +
>  		if (error)
>  			sdmac->status = old_status;
>  	}