[Intel-gfx] [PATCH] drm/i915: avoid false fence signaling when enabling preemption

[Chris Wilson]

Quoting Min He (2018-03-12 06:17:10)
> In i915_request_wait(), it adds a local intel_wait variable into rb tree
> of waiters. However, when the corresponding request is preempted, the
> seqno of this wait will not be updated, which will lead to a false
> signaling to the request and cause the i915_request_wait() to return
> early before the request is really completed.

Incorrect. We confirm that the request wasn't preempted before
signaling. Once i915_seqno_passed + intel_wait_check_request, we cannot
unsubmit the request.
-Chris