Re: [PATCH v3] dmaengine: sun6i: Fix potential deadlock on &sdev->lock

[Frank Li]

On Sun, Sep 27, 2026 at 12:10:49AM +0700, Nguyen Minh Tien wrote:
> From: Chengfeng Ye <dg573847474@xxxxxxxxx>
>
> As &sdev->lock is taken by the tasklet sun6i_dma_tasklet() in softirq
> context, other users of the lock in process context should disable
> interrupts, otherwise the tasklet can preempt a holder of the lock on
> the same CPU and deadlock. sun6i_dma_terminate_all() and
> sun6i_dma_pause() take it without disabling interrupts.
>
> This was found by an experimental static analysis tool for irq-related
> deadlocks. Lockdep reports it too on an Allwinner T113, where the lock
> is also taken inside the HARDIRQ-safe vc->lock:
>
>   [  299.389380] WARNING: possible irq lock inversion dependency detected
>   [  299.411196] c7109568 (&sdc->lock){+.-.}-{3:3}, at: sun6i_dma_terminate_all+0x40/0x2c4
>   [  299.419137] but this lock was taken by another, HARDIRQ-safe lock in the past:
>   [  299.426398]  (&vc->lock){-.-.}-{3:3}
>
> Use spin_lock_irqsave() in both places, as
> sun6i_dma_free_chan_resources() already does.
>
> Fixes: 555859308723 ("dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chengfeng Ye <dg573847474@xxxxxxxxx>
> [tien: rebased, added the lockdep report from a T113, Fixes and Cc stable]
> Signed-off-by: Nguyen Minh Tien <tien.nguyenminh@xxxxxxxxxxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

> I ran into this on a MangoPi MQ-Dual (Allwinner T113-S3): with lockdep
> on, stopping dmatest set off the report above in
> sun6i_dma_terminate_all(), and a small test module set it off in
> sun6i_dma_pause(). While looking for a fix I found Chengfeng's v2 from
> 2023. It never got a review and no longer applies, so I rebased it on
> dmaengine next and added the lockdep report, a Fixes tag and Cc stable.
> Chengfeng, I hope you don't mind me picking it up.
>
> With it, lockdep stays quiet on both paths on 7.3-rc4, and dmatest on
> four channels passes while another channel is paused, resumed and
> terminated in a loop.
>
> v2: https://lore.kernel.org/20230726051727.64088-1-dg573847474@xxxxxxxxx
>
>  drivers/dma/sun6i-dma.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index 5ad9d01cf..aee32363c 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -887,6 +887,7 @@ static int sun6i_dma_pause(struct dma_chan *chan)
>  	struct sun6i_dma_dev *sdev = to_sun6i_dma_dev(chan->device);
>  	struct sun6i_vchan *vchan = to_sun6i_vchan(chan);
>  	struct sun6i_pchan *pchan = vchan->phy;
> +	unsigned long flags;
>
>  	dev_dbg(dmaengine_chan_dev(chan), "vchan %p: pause\n", &vchan->vc);
>
> @@ -894,9 +895,9 @@ static int sun6i_dma_pause(struct dma_chan *chan)
>  		writel(DMA_CHAN_PAUSE_PAUSE,
>  		       pchan->base + DMA_CHAN_PAUSE);
>  	} else {
> -		spin_lock(&sdev->lock);
> +		spin_lock_irqsave(&sdev->lock, flags);
>  		list_del_init(&vchan->node);
> -		spin_unlock(&sdev->lock);
> +		spin_unlock_irqrestore(&sdev->lock, flags);
>  	}
>
>  	return 0;
> @@ -935,9 +936,9 @@ static int sun6i_dma_terminate_all(struct dma_chan *chan)
>  	unsigned long flags;
>  	LIST_HEAD(head);
>
> -	spin_lock(&sdev->lock);
> +	spin_lock_irqsave(&sdev->lock, flags);
>  	list_del_init(&vchan->node);
> -	spin_unlock(&sdev->lock);
> +	spin_unlock_irqrestore(&sdev->lock, flags);
>
>  	spin_lock_irqsave(&vchan->vc.lock, flags);
>
>
> base-commit: 0a8dda0a15d3926422d286567f945a05328a4ac6
> --
> 2.34.1
>