linux-kernel - Re: [PATCH] dmaengine: ptdma: fix concurrency issue with multiple dma transfer

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Date:   Tue, 18 Jan 2022 17:35:16 +0530
From:   Sanjay R Mehta <sanmehta@....com>
To:     Vinod Koul <vkoul@...nel.org>, Sanjay R Mehta <Sanju.Mehta@....com>
Cc:     gregkh@...uxfoundation.org, dan.j.williams@...el.com,
        Thomas.Lendacky@....com, robh@...nel.org,
        mchehab+samsung@...nel.org, davem@...emloft.net,
        linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH] dmaengine: ptdma: fix concurrency issue with multiple dma
 transfer



On 1/10/2022 1:27 PM, Sanjay R Mehta wrote:
> 
> 
> On 1/3/2022 5:04 PM, Vinod Koul wrote:
>> On 17-12-21, 03:58, Sanjay R Mehta wrote:
>>> From: Sanjay R Mehta <sanju.mehta@....com>
>>>
>>> The command should be submitted only if the engine is idle,
>>> for this, the next available descriptor is checked and set the flag
>>> to false in case the descriptor is non-empty.
>>>
>>> Also need to segregate the cases when DMA is complete or not.
>>> In case if DMA is already complete there is no need to handle it
>>> again and gracefully exit from the function.
>>>
>>> Signed-off-by: Sanjay R Mehta <sanju.mehta@....com>
>>> ---
>>>  drivers/dma/ptdma/ptdma-dmaengine.c | 24 +++++++++++++++++-------
>>>  1 file changed, 17 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/dma/ptdma/ptdma-dmaengine.c b/drivers/dma/ptdma/ptdma-dmaengine.c
>>> index c9e52f6..91b93e8 100644
>>> --- a/drivers/dma/ptdma/ptdma-dmaengine.c
>>> +++ b/drivers/dma/ptdma/ptdma-dmaengine.c
>>> @@ -100,12 +100,17 @@ static struct pt_dma_desc *pt_handle_active_desc(struct pt_dma_chan *chan,
>>>  		spin_lock_irqsave(&chan->vc.lock, flags);
>>>  
>>>  		if (desc) {
>>> -			if (desc->status != DMA_ERROR)
>>> -				desc->status = DMA_COMPLETE;
>>> -
>>> -			dma_cookie_complete(tx_desc);
>>> -			dma_descriptor_unmap(tx_desc);
>>> -			list_del(&desc->vd.node);
>>> +			if (desc->status != DMA_COMPLETE) {
>>> +				if (desc->status != DMA_ERROR)
>>> +					desc->status = DMA_COMPLETE;
>>> +
>>> +				dma_cookie_complete(tx_desc);
>>> +				dma_descriptor_unmap(tx_desc);
>>> +				list_del(&desc->vd.node);
>>> +			} else {
>>> +				/* Don't handle it twice */
>>> +				tx_desc = NULL;
>>> +			}
>>>  		}
>>>  
>>>  		desc = pt_next_dma_desc(chan);
>>> @@ -233,9 +238,14 @@ static void pt_issue_pending(struct dma_chan *dma_chan)
>>>  	struct pt_dma_chan *chan = to_pt_chan(dma_chan);
>>>  	struct pt_dma_desc *desc;
>>>  	unsigned long flags;
>>> +	bool engine_is_idle = true;
>>>  
>>>  	spin_lock_irqsave(&chan->vc.lock, flags);
>>>  
>>> +	desc = pt_next_dma_desc(chan);
>>> +	if (desc)
>>> +		engine_is_idle = false;
>>> +
>>>  	vchan_issue_pending(&chan->vc);
>>>  
>>>  	desc = pt_next_dma_desc(chan);
>>> @@ -243,7 +253,7 @@ static void pt_issue_pending(struct dma_chan *dma_chan)
>>>  	spin_unlock_irqrestore(&chan->vc.lock, flags);
>>>  
>>>  	/* If there was nothing active, start processing */
>>> -	if (desc)
>>> +	if (engine_is_idle)
>>
>> Can you explain why do you need this flag and why desc is not
>> sufficient..
> 
> Here it is required to know if the engine was idle or not before
> submitting new desc to the active list (i.e, before calling
> "vchan_issue_pending()" API). So that if there was nothing active then
> start processing this desc otherwise later.
> 
> Here desc is submitted to the engine after vchan_issue_pending() API
> called which will actually put the desc into the active list and then if
> I get the next desc, the condition will always be true. Therefore used
> this flag here to solve this issue.
> 
>>
>> It also sounds like 2 patches to me...
> 
> Once the desc is submitted to the engine that will be handled by
> pt_handle_active_desc() function. This issue was resolved by making
> these changes together. Hence kept into the single patch.
> 
> Please suggest to me, if this still needs to be split. I'll make the
> changes accordingly.
> 

Hi Vinod,

Any further comments for this patch? Need your help to get this upstreamed.


> - Sanjay
> 
>>
>>>  		pt_cmd_callback(desc, 0);
>>>  }
>>>  
>>> -- 
>>> 2.7.4
>>