[Bug 85888] [Bisected] stuck pageflip

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=85888

--- Comment #16 from Jim <jimmcdevitt60 at gmail.com> ---
Bisect in early - promised son Sunday.

I am now fairly befuddled. I did this process on three machines. On the twin of
this motherboard, a student did the bisection manually. On the machine I
reported I wrote a script to try all possible combinations of what was pushed
in rc1. When I came back to check, result was inconclusive. So. I looked a
little more closely to the patch Malcolm suggested (by itself, it didn't solve
my problem.)

Maybe my machines have different timings and maybe rc1 just exposed what was
there all along. I then re-applied Malcolms' patch and re-ran my script. What
it spit out was commit f0d3dad3. Lo and behold no more problem. The patch
description:

   Author: Chris Wilson <chris at chris-wilson.co.uk>
   Date:   Sun Sep 7 16:51:12 2014 +0100

       drm/i915: Wrap -EIO send-vblank event for failed pageflip in spinlock

       drm_send_vblank_event() demands that we hold the event spinlock whilst
       calling it, so do so.

Looking at the code tells me this can't be the problem. I then extracted a
fresh archive of rc1 and rc5 applied Malcolms' patch and reversed f0d3dad3. I
rebuilt the entire kernel for both rc1 and rc5. No problems. If i do not revert
f0d3dad3, I have the problem again. I installed the new rc1 kernel and also
tried the rc5 kernel. Both were fine. I ran piglit and no problems except the
the tests that always fail. So now, all 3 machines are happy.

All I want now is for somebody to explain to me WHY.

Thank you Malcolm for pointing me in the right direction.

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