Quoting Chris Wilson (2018-02-06 09:46:33)
> When a request is preempted, it is unsubmitted from the HW queue and
> removed from the active list of breadcrumbs. In the process, this
> however triggers the signaler and it may see the clear rbtree with the
> old, and still valid, seqno. This confuses the signaler into action and
> signaling the fence.
>
> Fixes: d6a2289d9d6b ("drm/i915: Remove the preempted request from the execution queue")
Testcase: igt/gem_exec_whisper/*-priority # reproducibility ~10%
-Chris