linux-kernel - Re: [PATCH] dmaengine: pl330: Acquire dmac's spinlock in pl330_tx

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Date:   Tue, 23 Aug 2016 10:08:31 -0700
From:   Guenter Roeck <groeck@...gle.com>
To:     Hsin-Yu Chao <hychao@...omium.org>
Cc:     smbarber@...omium.org, Guenter Roeck <groeck@...omium.org>,
        Vinod Koul <vinod.koul@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dmaengine: pl330: Acquire dmac's spinlock in pl330_tx_status

On Tue, Aug 23, 2016 at 2:16 AM, Hsin-Yu Chao <hychao@...omium.org> wrote:
> There is a racing when accessing dmac thread in pl330_tx_status that
> the pl330_update is handling active request at the same time and
> changing the status of descriptors. This could cause an invalid
> transferred count from BUSY descriptor added up to the residual number.
> Fix the bug by using the dmac's spinlock in pl330_tx_status to protect
> thread resources from changing.
> Note that the nested order of holding dmac's and dma_chan's spinlock is
> consistent with the rest of the driver: dma_chan first and then dmac,
> so it is safe from deadlock scenario.
>
> Signed-off-by: Hsin-Yu Chao <hychao@...omium.org>

Reviewed-by: Guenter Roeck <groeck@...omium.org>

> ---
>  drivers/dma/pl330.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 2449cb7..bd6861b 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2306,6 +2306,7 @@ pl330_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
>                 goto out;
>
>         spin_lock_irqsave(&pch->lock, flags);
> +       spin_lock(&pch->thread->dmac->lock);
>
>         if (pch->thread->req_running != -1)
>                 running = pch->thread->req[pch->thread->req_running].desc;
> @@ -2348,6 +2349,7 @@ pl330_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
>                 if (desc->last)
>                         residual = 0;
>         }
> +       spin_unlock(&pch->thread->dmac->lock);
>         spin_unlock_irqrestore(&pch->lock, flags);
>
>  out:
> --
> 2.8.0.rc3.226.g39d4020
>