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Message-ID: <9378e69f-2bd4-9d8d-c736-b8799f6ebecc@deltatee.com>
Date:   Wed, 26 Jul 2023 09:57:16 -0600
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To:     Chengfeng Ye <dg573847474@gmail.com>, vkoul@kernel.org
Cc:     dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230726104827.60382-1-dg573847474@gmail.com>
From:   Logan Gunthorpe <logang@deltatee.com>
In-Reply-To: <20230726104827.60382-1-dg573847474@gmail.com>
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Subject: Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on
 &plxdev->ring_lock
Precedence: bulk


On 2023-07-26 04:48, Chengfeng Ye wrote:
> As plx_dma_process_desc() is invoked by both tasklet plx_dma_desc_task()
> under softirq context and plx_dma_tx_status() callback that executed under
> process context, the lock aquicision of &plxdev->ring_lock inside
> plx_dma_process_desc() should disable irq otherwise deadlock could happen
> if the irq preempts the execution of process context code while the lock
> is held in process context on the same CPU.
> 
> Possible deadlock scenario:
> plx_dma_tx_status()
>     -> plx_dma_process_desc()
>     -> spin_lock(&plxdev->ring_lock)
>         <tasklet softirq>
>         -> plx_dma_desc_task()
>         -> plx_dma_process_desc()
>         -> spin_lock(&plxdev->ring_lock) (deadlock here)
> 
> This flaw was found by an experimental static analysis tool I am developing
> for irq-related deadlock.
> 
> The tentative patch fixes the potential deadlock by spin_lock_irqsave() in
> plx_dma_process_desc() to disable irq while lock is held.
> 
> Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>

Makes sense. Thanks!

Reviewed-by: Logan Gunthorpe <logang@deltatee.com>

Logan