Re: [PATCH] drm/core: Fail atomic IOCTL with no CRTC state but with signaling.
From: Harry Wentland
Date: Mon Jun 19 2017 - 11:35:53 EST
On 2017-06-09 05:30 PM, Andrey Grodzovsky wrote:
> While running IGT kms_atomic_transition test suite i encountered
> a hang in drmHandleEvent immidietly follwoing 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 singnaled.
> This point to a bug in IGT but also DRM should gracefully
> fail such scenario so no hang on user side will happen.
Can we create an IGT fix for this to make sure this won't happen?
> Explicitly fail by failing atomic_commit early in
> drm_mode_atomic_commit where such problem can be identified.
The change seems reasonable to me but I would like to see some input
from someone who's more familiar with the usermode side of things.
> Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@xxxxxxx>
> drivers/gpu/drm/drm_atomic.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index a567310..32eae1c 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++;
Not sure if intentional, but I like it.
> + /*
> + * 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;
> @@ -2179,6 +2188,8 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
Remove these extraneous newlines.
> ret = prepare_crtc_signaling(dev, state, arg, file_priv, &fence_state,
> if (ret)