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Message-ID: <ecf68b20-0a07-18bb-42a8-e622054b01f8@wanadoo.fr>
Date:   Wed, 26 Jul 2023 23:00:00 +0200
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Subject: Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on
 &plxdev->ring_lock
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To:     Logan Gunthorpe <logang@deltatee.com>,
        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>
 <9378e69f-2bd4-9d8d-c736-b8799f6ebecc@deltatee.com>
From:   Christophe JAILLET <christophe.jaillet@wanadoo.fr>
In-Reply-To: <9378e69f-2bd4-9d8d-c736-b8799f6ebecc@deltatee.com>
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Le 26/07/2023 à 17:57, Logan Gunthorpe a écrit :
> 
> 
> 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
> 

Hi,

as explained in another reply [1], would spin_lock_bh() be enough in 
such a case?

CJ

[1]: 
https://lore.kernel.org/all/5125e39b-0faf-63fc-0c51-982b2a567e21@wanadoo.fr/