On Mon, Jun 19, 2017 at 11:35:28AM -0400, Harry Wentland wrote:
> On 2017-06-09 05:30 PM, Andrey Grodzovsky wrote:
> > Problem:
> > While running IGT kms_atomic_transition test suite i encountered
> > a hang in drmHandleEvent immidietly follwoing an atomic_commit.
>
> s/immidietly/immediately/g
> s/follwoing/following/g
>
> > 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.
>
> s/singnaled/signaled/g
>
> > 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?
>
> > Fix:
> > 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.
I wonder if there's ever a case where it might be desirable to generate an event
from a commit without a crtc. I don't know if anyone has explicitly said that an
event can only be generated from state with crtc.
I usually don't mind letting userspace shoot itself in the foot, so keep that in
mind :)
Sean
>
> > Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky at amd.com>
> > ---
> > 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,
> > drm_mode_object_unreference(obj);
> > }
> >
> > +
> > +
>
> Remove these extraneous newlines.
>
> Harry
>
> > ret = prepare_crtc_signaling(dev, state, arg, file_priv, &fence_state,
> > &num_fences);
> > if (ret)
> >
--
Sean Paul, Software Engineer, Google / Chromium OS
