linux-kernel - Re: [PATCH] dmaengine: imx-sdma: fix deadlock in interrupt handler

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Message-ID: <20230925092004.natij4i364yupevi@pengutronix.de>
Date:   Mon, 25 Sep 2023 11:20:04 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Tim van der Staaij | Zign <Tim.vanderstaaij@...ngroup.com>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Fabio Estevam <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dmaengine: imx-sdma: fix deadlock in interrupt handler

Hello,

On Thu, Sep 21, 2023 at 09:57:11AM +0000, Tim van der Staaij | Zign wrote:
> dev_warn internally acquires the lock that is already held when
> sdma_update_channel_loop is called. Therefore it is acquired twice and
> this is detected as a deadlock. Temporarily release the lock while
> logging to avoid this.
> 
> Signed-off-by: Tim van der Staaij <tim.vanderstaaij@...ngroup.com>
> Link: https://lore.kernel.org/all/AM0PR08MB308979EC3A8A53AE6E2D3408802CA@AM0PR08MB3089.eurprd08.prod.outlook.com/
> ---
>  drivers/dma/imx-sdma.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 51012bd39900..3a7cd783a567 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -904,7 +904,10 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
>  	 * owned buffer is available (i.e. BD_DONE was set too late).
>  	 */
>  	if (sdmac->desc && !is_sdma_channel_enabled(sdmac->sdma, sdmac->channel)) {
> +		spin_unlock(&sdmac->vc.lock);
>  		dev_warn(sdmac->sdma->dev, "restart cyclic channel %d\n", sdmac->channel);
> +		spin_lock(&sdmac->vc.lock);
> +

I don't know if Sascha's patch helps, but this patch looks definitively
wrong. If this was the right approach (and I doubt it is) this
would definitively lack an explaining code comment.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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