Re: [PATCH v2] media: stm32-dcmi: fix lock scheme

[Hugues FRUCHET]

Hi Hans,

Problem was that lock was held while calling dmaengine APIs, which 
causes double lock issue when dma callback was called under context of 
dma_async_issue_pending() (see dcmi_start_dma() & below comments).
Rest of changes are around spin_lock() changed to spin_lock_irq() for 
safer lock management.

On 02/26/2018 02:56 PM, Hans Verkuil wrote:
> On 02/22/2018 10:49 AM, Hugues Fruchet wrote:
>> Fix lock scheme leading to spurious freeze.
> 
> Can you elaborate a bit more? It's hard to review since you don't
> describe what was wrong and why this fixes the problem.
> 
> Regards,
> 
> 	Hans
> 
>>
>> Signed-off-by: Hugues Fruchet <hugues.fruchet@xxxxxx>
>> ---
>> version 2:
>>    - dcmi_buf_queue() refactor to avoid to have "else" after "return"
>>      (warning detected by checkpatch.pl --strict -f stm32-dcmi.c)
>>
>>   drivers/media/platform/stm32/stm32-dcmi.c | 57 +++++++++++++------------------
>>   1 file changed, 24 insertions(+), 33 deletions(-)
>>
>> diff --git a/drivers/media/platform/stm32/stm32-dcmi.c b/drivers/media/platform/stm32/stm32-dcmi.c
>> index 2fd8bed..5de18ad 100644
>> --- a/drivers/media/platform/stm32/stm32-dcmi.c
>> +++ b/drivers/media/platform/stm32/stm32-dcmi.c
>> @@ -197,7 +197,7 @@ static void dcmi_dma_callback(void *param)
>>   	struct dma_tx_state state;
>>   	enum dma_status status;
>>   
>> -	spin_lock(&dcmi->irqlock);
>> +	spin_lock_irq(&dcmi->irqlock);
>>   
>>   	/* Check DMA status */
>>   	status = dmaengine_tx_status(chan, dcmi->dma_cookie, &state);
>> @@ -239,7 +239,7 @@ static void dcmi_dma_callback(void *param)
>>   				dcmi->errors_count++;
>>   				dcmi->active = NULL;
>>   
>> -				spin_unlock(&dcmi->irqlock);
>> +				spin_unlock_irq(&dcmi->irqlock);
>>   				return;
>>   			}
>>   
>> @@ -248,13 +248,11 @@ static void dcmi_dma_callback(void *param)
>>   
>>   			list_del_init(&dcmi->active->list);
>>   
>> -			if (dcmi_start_capture(dcmi)) {
>> +			spin_unlock_irq(&dcmi->irqlock);

Lock is released here before calling dcmi_start_capture() which calls 
dma_async_issue_pending()

>> +			if (dcmi_start_capture(dcmi))
>>   				dev_err(dcmi->dev, "%s: Cannot restart capture on DMA complete\n",
>>   					__func__);
>> -
>> -				spin_unlock(&dcmi->irqlock);
>> -				return;
>> -			}
>> +			return;
>>   		}
>>   
>>   		break;
>> @@ -263,7 +261,7 @@ static void dcmi_dma_callback(void *param)
>>   		break;
>>   	}
>>   
>> -	spin_unlock(&dcmi->irqlock);
>> +	spin_unlock_irq(&dcmi->irqlock);
>>   }
>>   
>>   static int dcmi_start_dma(struct stm32_dcmi *dcmi,
>> @@ -360,7 +358,7 @@ static irqreturn_t dcmi_irq_thread(int irq, void *arg)
>>   {
>>   	struct stm32_dcmi *dcmi = arg;
>>   
>> -	spin_lock(&dcmi->irqlock);
>> +	spin_lock_irq(&dcmi->irqlock);
>>   
>>   	/* Stop capture is required */
>>   	if (dcmi->state == STOPPING) {
>> @@ -370,7 +368,7 @@ static irqreturn_t dcmi_irq_thread(int irq, void *arg)
>>   
>>   		complete(&dcmi->complete);
>>   
>> -		spin_unlock(&dcmi->irqlock);
>> +		spin_unlock_irq(&dcmi->irqlock);
>>   		return IRQ_HANDLED;
>>   	}
>>   
>> @@ -383,35 +381,34 @@ static irqreturn_t dcmi_irq_thread(int irq, void *arg)
>>   			 __func__);
>>   
>>   		dcmi->errors_count++;
>> -		dmaengine_terminate_all(dcmi->dma_chan);
>> -
>>   		dev_dbg(dcmi->dev, "Restarting capture after DCMI error\n");
>>   
>> -		if (dcmi_start_capture(dcmi)) {
>> +		spin_unlock_irq(&dcmi->irqlock);
Lock is released here before calling dma APIs (terminate then 
async_issue_pending)

>> +		dmaengine_terminate_all(dcmi->dma_chan);
>> +
>> +		if (dcmi_start_capture(dcmi))
>>   			dev_err(dcmi->dev, "%s: Cannot restart capture on overflow or error\n",
>>   				__func__);
>> -
>> -			spin_unlock(&dcmi->irqlock);
>> -			return IRQ_HANDLED;
>> -		}
>> +		return IRQ_HANDLED;
>>   	}
>>   
>> -	spin_unlock(&dcmi->irqlock);
>> +	spin_unlock_irq(&dcmi->irqlock);
>>   	return IRQ_HANDLED;
>>   }
>>   
>>   static irqreturn_t dcmi_irq_callback(int irq, void *arg)
>>   {
>>   	struct stm32_dcmi *dcmi = arg;
>> +	unsigned long flags;
>>   
>> -	spin_lock(&dcmi->irqlock);
>> +	spin_lock_irqsave(&dcmi->irqlock, flags);
>>   
>>   	dcmi->misr = reg_read(dcmi->regs, DCMI_MIS);
>>   
>>   	/* Clear interrupt */
>>   	reg_set(dcmi->regs, DCMI_ICR, IT_FRAME | IT_OVR | IT_ERR);
>>   
>> -	spin_unlock(&dcmi->irqlock);
>> +	spin_unlock_irqrestore(&dcmi->irqlock, flags);
>>   
>>   	return IRQ_WAKE_THREAD;
>>   }
>> @@ -490,9 +487,8 @@ static void dcmi_buf_queue(struct vb2_buffer *vb)
>>   	struct stm32_dcmi *dcmi =  vb2_get_drv_priv(vb->vb2_queue);
>>   	struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
>>   	struct dcmi_buf *buf = container_of(vbuf, struct dcmi_buf, vb);
>> -	unsigned long flags = 0;
>>   
>> -	spin_lock_irqsave(&dcmi->irqlock, flags);
>> +	spin_lock_irq(&dcmi->irqlock);
>>   
>>   	if ((dcmi->state == RUNNING) && (!dcmi->active)) {
>>   		dcmi->active = buf;
>> @@ -500,19 +496,15 @@ static void dcmi_buf_queue(struct vb2_buffer *vb)
>>   		dev_dbg(dcmi->dev, "Starting capture on buffer[%d] queued\n",
>>   			buf->vb.vb2_buf.index);
>>   
>> -		if (dcmi_start_capture(dcmi)) {
>> +		spin_unlock_irq(&dcmi->irqlock);
Lock is released here before calling dma APIs (terminate then 
async_issue_pending)

>> +		if (dcmi_start_capture(dcmi))
>>   			dev_err(dcmi->dev, "%s: Cannot restart capture on overflow or error\n",
>>   				__func__);
>> -
>> -			spin_unlock_irqrestore(&dcmi->irqlock, flags);
>> -			return;
>> -		}
>>   	} else {
>>   		/* Enqueue to video buffers list */
>>   		list_add_tail(&buf->list, &dcmi->buffers);
>> +		spin_unlock_irq(&dcmi->irqlock);
>>   	}
>> -
>> -	spin_unlock_irqrestore(&dcmi->irqlock, flags);
>>   }
>>   
>>   static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
>> @@ -598,20 +590,17 @@ static int dcmi_start_streaming(struct vb2_queue *vq, unsigned int count)
>>   
>>   	dev_dbg(dcmi->dev, "Start streaming, starting capture\n");
>>   
>> +	spin_unlock_irq(&dcmi->irqlock);
>>   	ret = dcmi_start_capture(dcmi);
>>   	if (ret) {
>>   		dev_err(dcmi->dev, "%s: Start streaming failed, cannot start capture\n",
>>   			__func__);
>> -
>> -		spin_unlock_irq(&dcmi->irqlock);
>>   		goto err_subdev_streamoff;
>>   	}
>>   
>>   	/* Enable interruptions */
>>   	reg_set(dcmi->regs, DCMI_IER, IT_FRAME | IT_OVR | IT_ERR);
>>   
>> -	spin_unlock_irq(&dcmi->irqlock);
>> -
>>   	return 0;
>>   
>>   err_subdev_streamoff:
>> @@ -654,7 +643,9 @@ static void dcmi_stop_streaming(struct vb2_queue *vq)
>>   		dev_err(dcmi->dev, "%s: Failed to stop streaming, subdev streamoff error (%d)\n",
>>   			__func__, ret);
>>   
>> +	spin_lock_irq(&dcmi->irqlock);
>>   	dcmi->state = STOPPING;
>> +	spin_unlock_irq(&dcmi->irqlock);
>>   
>>   	timeout = wait_for_completion_interruptible_timeout(&dcmi->complete,
>>   							    time_ms);
>>
> 

Best regards,
Hugues.