[PATCH 4/4] dmaengine: xilinx_dma: Add device synchronisation callback

[Lars-Peter Clausen]

On 4/23/21 3:19 AM, Adrian Larumbe wrote:
> This was required as an answer to a very unusual race condition, whereby a
> thread waiting on a completion signaled in a callback triggered by
> dmaengine_desc_callback_invoke might immediately attempt to release the
> DMA channel whilst the channel lock was still free. This would cause the
> remaining descriptors to be deallocated, and xilinx_dma_chan_desc_cleanup
> to perform an invalid memory access when attempting to traverse the rest
> of the channel's done_list.
>
> Now, when releasing a DMA channel, it will wait until the tasklet has
> finished.
>
> Signed-off-by: Adrian Larumbe <adrian.martinezlarumbe at imgtec.com>

Hi,


Patch looks good, but basically the same got already applied a few weeks 
ago.

See 
https://git.kernel.org/pub/scm/linux/kernel/git/vkoul/dmaengine.git/commit/?h=next&id=50db2050faf854cbaf4b6557a7a8ca21bff302ae

- Lars

> ---
>   drivers/dma/xilinx/xilinx_dma.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index 40c6cf8bf0e6..d4bad999e7f9 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -942,6 +942,13 @@ static void xilinx_dma_free_chan_resources(struct dma_chan *dchan)
>   
>   }
>   
> +static void xilinx_dma_synchronize(struct dma_chan *dchan)
> +{
> +	struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
> +
> +	tasklet_kill(&chan->tasklet);
> +}
> +
>   /**
>    * xilinx_dma_get_residue - Compute residue for a given descriptor
>    * @chan: Driver specific dma channel
> @@ -3235,6 +3242,7 @@ static int xilinx_dma_probe(struct platform_device *pdev)
>   	xdev->common.device_tx_status = xilinx_dma_tx_status;
>   	xdev->common.device_issue_pending = xilinx_dma_issue_pending;
>   	xdev->common.device_config = xilinx_dma_slave_config;
> +	xdev->common.device_synchronize = xilinx_dma_synchronize;
>   	if (xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
>   		dma_cap_set(DMA_CYCLIC, xdev->common.cap_mask);
>   		xdev->common.device_prep_slave_sg = xilinx_dma_prep_slave_sg;