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Date: Fri, 15 Apr 2016 09:47:45 +0200
From: Daniel Vetter <daniel@ffwll.ch>
To: Gustavo Padovan <gustavo@padovan.org>
Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Daniel Stone <daniels@collabora.com>,
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        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Subject: Re: [RFC 3/8] drm/fence: allow fence waiting to be interrupted by
 userspace
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On Thu, Apr 14, 2016 at 06:29:36PM -0700, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> If userspace is running an synchronously atomic commit and interrupts the
> atomic operation during fence_wait() it will hang until the timer expires,
> so here we change the wait to be interruptible so it stop immediately when
> userspace wants to quit.
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 7bf678e..f85ef8c 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1007,7 +1007,7 @@ void drm_atomic_helper_wait_for_fences(struct drm_device *dev,
>  
>  		WARN_ON(!plane->state->fb);
>  
> -		fence_wait(plane->state->fence, false);
> +		fence_wait(plane->state->fence, true);

You need to propagate the error code when allowing the wait to be
interrupted - we can't proceed with the atomic update in that case, but
need to bail out. And userspace needs to restart the ioctl.

Also, needs a testcase I think.
-Daniel

>  		fence_put(plane->state->fence);
>  		plane->state->fence = NULL;
>  	}
> -- 
> 2.5.5
> 

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