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

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Date:   Wed, 26 Jul 2023 23:00:00 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Chengfeng Ye <dg573847474@...il.com>, vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: plx_dma: Fix potential deadlock on
 &plxdev->ring_lock

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@...il.com>
> 
> Makes sense. Thanks!
> 
> Reviewed-by: Logan Gunthorpe <logang@...tatee.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/