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Date:   Mon, 25 Sep 2023 11:20:04 +0200
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Tim van der Staaij | Zign <Tim.vanderstaaij@zigngroup.com>
Cc:     Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Vinod Koul <vkoul@kernel.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        "dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
        Fabio Estevam <festevam@gmail.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] dmaengine: imx-sdma: fix deadlock in interrupt handler
Message-ID: <20230925092004.natij4i364yupevi@pengutronix.de>
References: <AM0PR08MB30897429213E8DB9BCC1D6C880F8A@AM0PR08MB3089.eurprd08.prod.outlook.com>
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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.
>=20
> Signed-off-by: Tim van der Staaij <tim.vanderstaaij@zigngroup.com>
> Link: https://lore.kernel.org/all/AM0PR08MB308979EC3A8A53AE6E2D3408802CA@=
AM0PR08MB3089.eurprd08.prod.outlook.com/
> ---
>  drivers/dma/imx-sdma.c | 3 +++
>  1 file changed, 3 insertions(+)
>=20
> 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_cha=
nnel *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->chann=
el);
> +		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

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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