linux-kernel - Re: [RFC 3/8] drm/fence: allow fence waiting to be interrupted by userspace

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Date:	Fri, 15 Apr 2016 09:47:45 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Gustavo Padovan <gustavo@...ovan.org>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Stone <daniels@...labora.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	laurent.pinchart@...asonboard.com, seanpaul@...gle.com,
	marcheu@...gle.com, m.chehab@...sung.com,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
Subject: Re: [RFC 3/8] drm/fence: allow fence waiting to be interrupted by
 userspace

On Thu, Apr 14, 2016 at 06:29:36PM -0700, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.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@...labora.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