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

[Chengfeng Ye]

On Sun, Sep 27, 2026 at 1:10 AM Nguyen Minh Tien
<tien.nguyenminh@xxxxxxxxxxxxxxxxxx> 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>
> ---
> 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.


Not at all, thanks for picking this three-year-old patch up and
testing it on hardware. I’m glad to see the patch can move forward.

Best regards,
Chengfeng