linux-kernel - Re: [PATCH v2] drm/core: Fail atomic IOCTL with no CRTC state but with signaling.

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Date:   Mon, 26 Jun 2017 15:44:07 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Andrey Grodzovsky <Andrey.Grodzovsky@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, maarten.lankhorst@...ux.intel.com
Cc:     amd-gfx@...ts.freedesktop.org, seanpaul@...omium.org,
        daniel@...ll.ch
Subject: Re: [PATCH v2] drm/core: Fail atomic IOCTL with no CRTC state but
 with signaling.

On 2017-06-20 01:57 PM, Andrey Grodzovsky wrote:
> Problem : While running IGT kms_atomic_transition test suite i encountered
> a hang in drmHandleEvent immediately following  an atomic_commit.
> After dumping the atomic state I relized that in this case there was
> not even one CRTC attached to the state and only disabled
> planes. This probably due to a commit which hadn't changed any property
> which would require attaching crtc state. This means drmHandleEvent
> will never wake up from read since without CRTC in atomic state
> the event fd will not be signaled.
> 
> Fix: Protect against this issue by failing atomic_commit early in
> drm_mode_atomic_commit where such probelm can be identified.
> 
> v2:
> Fix typos and extra newlines.
> 
> Change-Id: I3ee28ffae35fd1e8bfe553146c44da53da02e6f8
> Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@....com>

Reviewed-by: Harry Wentland <harry.wentland@....com>

Harry

> ---
>  drivers/gpu/drm/drm_atomic.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index a567310..48145bf 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -1933,7 +1933,7 @@ static int prepare_crtc_signaling(struct drm_device *dev,
>  {
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *crtc_state;
> -	int i, ret;
> +	int i, c = 0, ret;
>  
>  	if (arg->flags & DRM_MODE_ATOMIC_TEST_ONLY)
>  		return 0;
> @@ -1994,8 +1994,17 @@ static int prepare_crtc_signaling(struct drm_device *dev,
>  
>  			crtc_state->event->base.fence = fence;
>  		}
> +
> +		c++;
>  	}
>  
> +	/*
> +	 * Having this flag means user mode pends on event which will never
> +	 * reach due to lack of at least one CRTC for signaling
> +	 */
> +	if (c == 0 && (arg->flags & DRM_MODE_PAGE_FLIP_EVENT))
> +		return -EINVAL;
> +
>  	return 0;
>  }
>  
>