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

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Date:   Wed, 28 Jun 2017 12:23:06 +0200
From:   Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:     Harry Wentland <harry.wentland@....com>,
        Andrey Grodzovsky <Andrey.Grodzovsky@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        seanpaul@...omium.org
Subject: Re: [PATCH v2] drm/core: Fail atomic IOCTL with no CRTC state but
 with signaling.

Op 27-06-17 om 17:01 schreef Daniel Vetter:
> On Tue, Jun 27, 2017 at 04:29:44PM +0200, Maarten Lankhorst wrote:
>> Op 27-06-17 om 09:37 schreef Daniel Vetter:
>>> On Mon, Jun 26, 2017 at 03:44:07PM -0400, Harry Wentland wrote:
>>>> 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>
>>> Stalling on this hoping for the igt patch. Does it exist already?
>>> -Daniel
>>>
>>>> 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;
>>>>>  }
>>>>>  
>>>>>
>> Just do it, and I'll commit this to igt?
> Ack on both the kernel patch and the igt patch, feel free to push them
> both with:
>
> Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>
>
> If you do, please add the Testcase: line to the kernel patch.
Oops, missed adding the testcase to commit message, but pushed.

I've pushed the IGT testcase as well, after fixing it up to make sure it works as intended.

~Maarten