[PATCH 1/2] drm: refernce count event->completion

[Maarten Lankhorst]

Op 21-12-16 om 11:36 schreef Chris Wilson:
> 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
>> evevntually 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
>
afaict crtc commit is already taken to wait for completion, so this patch makes sense.

There's just a minor typo in the subject. :)
Not sure that release_commit should be a function pointer, regardless..

Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>