linux-kernel - Re: [PATCH v2] dmaengine: plx_dma: Fix potential deadlock on &plxdev->ring

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Message-ID: <ff871e8d-c5b0-99ed-0a44-385d70c503c2@deltatee.com>
Date:   Sun, 30 Jul 2023 17:50:32 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Chengfeng Ye <dg573847474@...il.com>, vkoul@...nel.org
Cc:     yuyunbo519@...il.com, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, christophe.jaillet@...adoo.fr
Subject: Re: [PATCH v2] dmaengine: plx_dma: Fix potential deadlock on
 &plxdev->ring_lock



On 7/29/23 11:59, 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 lock was changed from spin_lock_bh() to spin_lock() by a previous patch
> for performance concern but unintentionally brought this potential deadlock
> problem.
> 
> This patch reverts back to spin_lock_bh() to fix the deadlock problem.
> 
> Fixes: 1d05a0bdb420 ("dmaengine: plx_dma: Move spin_lock_bh() to spin_lock()")
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>
> 

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

Thanks!

Logan