linux-kernel - Re: [PATCH v3 6/9] dma-buf/fence-array: Add fence deadline support

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Message-ID: <YTj6S1yVvBPAZ9RJ@phenom.ffwll.local>
Date:   Wed, 8 Sep 2021 20:00:43 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        "open list:SYNC FILE FRAMEWORK" <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 6/9] dma-buf/fence-array: Add fence deadline support

On Fri, Sep 03, 2021 at 11:47:57AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/dma-buf/dma-fence-array.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/dma-buf/dma-fence-array.c b/drivers/dma-buf/dma-fence-array.c
> index d3fbd950be94..8d194b09ee3d 100644
> --- a/drivers/dma-buf/dma-fence-array.c
> +++ b/drivers/dma-buf/dma-fence-array.c
> @@ -119,12 +119,23 @@ static void dma_fence_array_release(struct dma_fence *fence)
>  	dma_fence_free(fence);
>  }
>  
> +static void dma_fence_array_set_deadline(struct dma_fence *fence,
> +					 ktime_t deadline)
> +{
> +	struct dma_fence_array *array = to_dma_fence_array(fence);
> +	unsigned i;
> +
> +	for (i = 0; i < array->num_fences; ++i)
> +		dma_fence_set_deadline(array->fences[i], deadline);

Hm I wonder whether this can go wrong, and whether we need Christian's
massive fence iterator that I've seen flying around. If you nest these
things too much it could all go wrong I think. I looked at other users
which inspect dma_fence_array and none of them have a risk for unbounded
recursion.

Maybe check with Christian.
-Daniel


> +}
> +
>  const struct dma_fence_ops dma_fence_array_ops = {
>  	.get_driver_name = dma_fence_array_get_driver_name,
>  	.get_timeline_name = dma_fence_array_get_timeline_name,
>  	.enable_signaling = dma_fence_array_enable_signaling,
>  	.signaled = dma_fence_array_signaled,
>  	.release = dma_fence_array_release,
> +	.set_deadline = dma_fence_array_set_deadline,
>  };
>  EXPORT_SYMBOL(dma_fence_array_ops);
>  
> -- 
> 2.31.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch