Re: [PATCH v2 1/2] dmaengine: xilinx: dpdma: Fix race condition in vsync IRQ

[Tomi Valkeinen]

Hi,

On 28/02/2024 06:21, Vishal Sagar wrote:
> From: Neel Gandhi <neel.gandhi@xxxxxxxxxx>
>
> The vchan_next_desc() function, called from
> xilinx_dpdma_chan_queue_transfer(), must be called with
> virt_dma_chan.lock held. This isn't correctly handled in all code paths,
> resulting in a race condition between the .device_issue_pending()
> handler and the IRQ handler which causes DMA to randomly stop. Fix it by
> taking the lock around xilinx_dpdma_chan_queue_transfer() calls that are
> missing it.
>
> Signed-off-by: Neel Gandhi <neel.gandhi@xxxxxxx>
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> Signed-off-by: Vishal Sagar <vishal.sagar@xxxxxxx>
>
> Link: https://lore.kernel.org/all/20220122121407.11467-1-neel.gandhi@xxxxxxxxxx
> ---
>   drivers/dma/xilinx/xilinx_dpdma.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)

This fixes a lockdep warning:

WARNING: CPU: 1 PID: 466 at drivers/dma/xilinx/xilinx_dpdma.c:834

Afaics, this issue has been around since the initial commit, in v5.10, 
and the fix applies on top of v5.10. I have tested this on v6.2, which 
is where the DP support was added to the board I have.

So I think you can add:

Fixes: 7cbb0c63de3f ("dmaengine: xilinx: dpdma: Add the Xilinx 
DisplayPort DMA engine driver")

 Tomi

> diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c
> index b82815e64d24..28d9af8f00f0 100644
> --- a/drivers/dma/xilinx/xilinx_dpdma.c
> +++ b/drivers/dma/xilinx/xilinx_dpdma.c
> @@ -1097,12 +1097,14 @@ static void xilinx_dpdma_chan_vsync_irq(struct  xilinx_dpdma_chan *chan)
>   	 * Complete the active descriptor, if any, promote the pending
>   	 * descriptor to active, and queue the next transfer, if any.
>   	 */
> +	spin_lock(&chan->vchan.lock);
>   	if (chan->desc.active)
>   		vchan_cookie_complete(&chan->desc.active->vdesc);
>   	chan->desc.active = pending;
>   	chan->desc.pending = NULL;
>   
>   	xilinx_dpdma_chan_queue_transfer(chan);
> +	spin_unlock(&chan->vchan.lock);
>   
>   out:
>   	spin_unlock_irqrestore(&chan->lock, flags);
> @@ -1264,10 +1266,12 @@ static void xilinx_dpdma_issue_pending(struct dma_chan *dchan)
>   	struct xilinx_dpdma_chan *chan = to_xilinx_chan(dchan);
>   	unsigned long flags;
>   
> -	spin_lock_irqsave(&chan->vchan.lock, flags);
> +	spin_lock_irqsave(&chan->lock, flags);
> +	spin_lock(&chan->vchan.lock);
>   	if (vchan_issue_pending(&chan->vchan))
>   		xilinx_dpdma_chan_queue_transfer(chan);
> -	spin_unlock_irqrestore(&chan->vchan.lock, flags);
> +	spin_unlock(&chan->vchan.lock);
> +	spin_unlock_irqrestore(&chan->lock, flags);
>   }
>   
>   static int xilinx_dpdma_config(struct dma_chan *dchan,
> @@ -1495,7 +1499,9 @@ static void xilinx_dpdma_chan_err_task(struct tasklet_struct *t)
>   		    XILINX_DPDMA_EINTR_CHAN_ERR_MASK << chan->id);
>   
>   	spin_lock_irqsave(&chan->lock, flags);
> +	spin_lock(&chan->vchan.lock);
>   	xilinx_dpdma_chan_queue_transfer(chan);
> +	spin_unlock(&chan->vchan.lock);
>   	spin_unlock_irqrestore(&chan->lock, flags);
>   }
>