Quoting Tvrtko Ursulin (2018-02-05 09:34:48)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Commit 99e48bf98dd0 ("drm/i915: Lock out execlist tasklet while peeking
> inside for busy-stats") added a tasklet_disable call in busy stats
> enabling, but we failed to understand that the PMU enable callback runs
> as an hard IRQ (IPI).
>
> Consequence of this is that the PMU enable callback can interrupt the
> execlists tasklet, and will then deadlock when it calls
> intel_engine_stats_enable->tasklet_disable.
>
> To fix this, I realized it is possible to move the engine stats enablement
> and disablement to PMU event init and destroy hooks. This allows for much
> simpler implementation since those hooks run in normal context (can
> sleep).
>
> v2: Extract engine_event_destroy. (Chris Wilson)
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Fixes: 99e48bf98dd0 ("drm/i915: Lock out execlist tasklet while peeking inside for busy-stats")
> Testcase: igt/perf_pmu/enable-race-*
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
I didn't have any nightmares about this,
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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