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

[Jim Rees]

Daniel Vetter wrote:

  Latest report just says that the revert isn't helping either. I suspect
  the report is a giantic conflagration of everything ever that kills
  various reporters boxes. I still believe that the patch here fixes the
  original bug, but there might be a lot more hiding.
  
  It's at least seen quite a pile of testing, so I think it's sounds, and we
  could cherry-pick it to dinf with cc: stable for 4.9+. Worst case it's not
  going to help for the other problems.

No, that's not what the latest report says. It says, "running for 2 weeks
... This is certainly way, way better than the current stock experience,
which results in my T460s entirely locking up daily." and "Less than a day
after I made that comment I got a hard lockup". So reverting the buggy
helper nonblock tracking commit took this reporter from locking up daily to
locking up once in two weeks. For everyone else, reverting the buggy commit
fixes all bugs. Also note that this most recent lockup appears to be a
different bug ("GPU HANG: ecode").

So we have a commit that is causing hard lockups and flip_done timeouts for
multiple users. Reverting this commit fixes the problem. But we did not push
the revert up for 4.9, and it looks like we're not going to push it up for
4.10 either.