On Wed, Dec 21, 2016 at 11:23:30AM +0100, Daniel Vetter wrote: > When writing the generic nonblocking commit code I assumed that > through clever lifetime management I can assure that the completion > (stored in drm_crtc_commit) only gets freed after it is completed. And > that worked. > > I also wanted to make nonblocking helpers resilient against driver > bugs, by having timeouts everywhere. And that worked too. > > Unfortunately taking boths things together results in oopses :( Well, > at least sometimes: What seems to happen is that the drm event hangs > around forever stuck in limbo land. The nonblocking helpers eventually > time out, move on and release it. Now the bug I tested all this > against is drivers that just entirely fail to deliver the vblank > events like they should, and in those cases the event is simply > leaked. But what seems to happen, at least sometimes, on i915 is that > the event is set up correctly, but somohow the vblank fails to fire in > time. Which means the event isn't leaked, it's still there waiting for > eventually a vblank to fire. That tends to happen when re-enabling the > pipe, and then the trap springs and the kernel oopses. > > The correct fix here is simply to refcount the crtc commit to make > sure that the event sticks around even for drivers which only > sometimes fail to deliver vblanks for some arbitrary reasons. Since > crtc commits are already refcounted that's easy to do.
Or make the event a part of the atomic state? -Chris -- Chris Wilson, Intel Open Source Technology Centre
