linux-kernel - Re: [PATCH v1 2/2] drm: Clear the fence pointer when writeback job signaled

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Message-ID: <20190731131525.vjnkbnbatb5tbuzh@e110455-lin.cambridge.arm.com>
Date:   Wed, 31 Jul 2019 14:15:25 +0100
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     "Lowry Li (Arm Technology China)" <Lowry.Li@....com>
Cc:     "james qian wang (Arm Technology China)" <james.qian.wang@....com>,
        "maarten.lankhorst@...ux.intel.com" 
        <maarten.lankhorst@...ux.intel.com>,
        "seanpaul@...omium.org" <seanpaul@...omium.org>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        Brian Starkey <Brian.Starkey@....com>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@....com>,
        "maxime.ripard@...tlin.com" <maxime.ripard@...tlin.com>,
        "eric@...olt.net" <eric@...olt.net>,
        "kieran.bingham+renesas@...asonboard.com" 
        <kieran.bingham+renesas@...asonboard.com>,
        "sean@...rly.run" <sean@...rly.run>,
        "laurent.pinchart@...asonboard.com" 
        <laurent.pinchart@...asonboard.com>,
        "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@....com>,
        Ayan Halder <Ayan.Halder@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>, nd <nd@....com>
Subject: Re: [PATCH v1 2/2] drm: Clear the fence pointer when writeback job
 signaled

Hi Lowry,

On Wed, Jul 31, 2019 at 11:04:45AM +0000, Lowry Li (Arm Technology China) wrote:
> During it signals the completion of a writeback job, after releasing
> the out_fence, we'd clear the pointer.
> 
> Check if fence left over in drm_writeback_cleanup_job(), release it.
> 
> Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@....com>
> ---
>  drivers/gpu/drm/drm_writeback.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_writeback.c b/drivers/gpu/drm/drm_writeback.c
> index ff138b6..43d9e3b 100644
> --- a/drivers/gpu/drm/drm_writeback.c
> +++ b/drivers/gpu/drm/drm_writeback.c
> @@ -324,6 +324,9 @@ void drm_writeback_cleanup_job(struct drm_writeback_job *job)
>  	if (job->fb)
>  		drm_framebuffer_put(job->fb);
>  
> +	if (job->out_fence)
> +		dma_fence_put(job->out_fence);
> +
>  	kfree(job);
>  }

This change looks good.

>  EXPORT_SYMBOL(drm_writeback_cleanup_job);
> @@ -366,25 +369,29 @@ static void cleanup_work(struct work_struct *work)
>  {
>  	unsigned long flags;
>  	struct drm_writeback_job *job;
> +	struct dma_fence *out_fence;
>  
>  	spin_lock_irqsave(&wb_connector->job_lock, flags);
>  	job = list_first_entry_or_null(&wb_connector->job_queue,
>  				       struct drm_writeback_job,
>  				       list_entry);
> -	if (job) {
> +	if (job)
>  		list_del(&job->list_entry);
> -		if (job->out_fence) {
> -			if (status)
> -				dma_fence_set_error(job->out_fence, status);
> -			dma_fence_signal(job->out_fence);
> -			dma_fence_put(job->out_fence);

*Here*

> -		}
> -	}
> +
>  	spin_unlock_irqrestore(&wb_connector->job_lock, flags);
>  
>  	if (WARN_ON(!job))
>  		return;
>  
> +	out_fence = job->out_fence;
> +	if (out_fence) {
> +		if (status)
> +			dma_fence_set_error(out_fence, status);
> +		dma_fence_signal(out_fence);
> +		dma_fence_put(out_fence);
> +		job->out_fence = NULL;
> +	}
> +

I don't get the point of this change. Why not just add job->out_fence = NULL
where *Here* is?

Best regards,
Liviu 

>  	INIT_WORK(&job->cleanup_work, cleanup_work);
>  	queue_work(system_long_wq, &job->cleanup_work);
>  }
> -- 
> 1.9.1
> 

-- 
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