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

[Sascha Hauer]

Hi Tim,

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@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/AM0PR08MB308979EC3A8A53AE6E2D3408802CA@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> ---
>  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);

This is strange. Why and how does dev_warn() call back into the SDMA
driver?

We shouldn't merge this without having a clue what exactly goes wrong
here. Please provide the corresponding lockdep output.

Sascha

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