Re: [PATCH] dmaengine: mediatek: Fix a flag reuse error in mtk_cqdma_tx_status()

[Eugen Hristev <eugen.hristev@linaro.org>]

On 6/6/25 10:17, Qiu-ji Chen wrote:
> Fixed a flag reuse bug in the mtk_cqdma_tx_status() function.
> 
> Fixes: 157ae5ffd76a ("dmaengine: mediatek: Fix a possible deadlock error in mtk_cqdma_tx_status()")
> Cc: stable@vger.kernel.org
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202505270641.MStzJUfU-lkp@intel.com/
> Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
> ---
>  drivers/dma/mediatek/mtk-cqdma.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/dma/mediatek/mtk-cqdma.c b/drivers/dma/mediatek/mtk-cqdma.c
> index 47c8adfdc155..f7b870d2ca90 100644
> --- a/drivers/dma/mediatek/mtk-cqdma.c
> +++ b/drivers/dma/mediatek/mtk-cqdma.c
> @@ -441,18 +441,19 @@ static enum dma_status mtk_cqdma_tx_status(struct dma_chan *c,
>  	struct mtk_cqdma_vdesc *cvd;
>  	struct virt_dma_desc *vd;
>  	enum dma_status ret;
> -	unsigned long flags;
> +	unsigned long pc_flags;
> +	unsigned long vc_flags;
>  	size_t bytes = 0;
>  
>  	ret = dma_cookie_status(c, cookie, txstate);
>  	if (ret == DMA_COMPLETE || !txstate)
>  		return ret;
>  
> -	spin_lock_irqsave(&cvc->pc->lock, flags);
> -	spin_lock_irqsave(&cvc->vc.lock, flags);
> +	spin_lock_irqsave(&cvc->pc->lock, pc_flags);
> +	spin_lock_irqsave(&cvc->vc.lock, vc_flags);
>  	vd = mtk_cqdma_find_active_desc(c, cookie);
> -	spin_unlock_irqrestore(&cvc->vc.lock, flags);
> -	spin_unlock_irqrestore(&cvc->pc->lock, flags);
> +	spin_unlock_irqrestore(&cvc->vc.lock, vc_flags);
> +	spin_unlock_irqrestore(&cvc->pc->lock, pc_flags);
>  
>  	if (vd) {
>  		cvd = to_cqdma_vdesc(vd);

If the first spin_lock_irqsave already saved the irq flags and disabled
them, would it be meaningful to actually use a simple spin_lock for the
second lock ? Or rather spin_lock_nested since there is a second nested
lock taken ?

Eugen