Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Since the execlists_active() is no longer protected by the
> engine->active.lock, we need to protect the request pointer with RCU to
> prevent it being freed as we evaluate whether or not we need to preempt.
>
> Fixes: df403069029d ("drm/i915/execlists: Lift process_csb() out of the irq-off spinlock")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_scheduler.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
> index d2edb527dcb8..010d67f48ad9 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler.c
> +++ b/drivers/gpu/drm/i915/i915_scheduler.c
> @@ -202,21 +202,26 @@ static void kick_submission(struct intel_engine_cs *engine,
> if (prio <= engine->execlists.queue_priority_hint)
> return;
>
> + rcu_read_lock();
> +
> /* Nothing currently active? We're overdue for a submission! */
> inflight = execlists_active(&engine->execlists);
> if (!inflight)
> - return;
> + goto unlock;
>
> /*
> * If we are already the currently executing context, don't
> * bother evaluating if we should preempt ourselves.
> */
> if (inflight->hw_context == rq->hw_context)
> - return;
> + goto unlock;
>
> engine->execlists.queue_priority_hint = prio;
> if (need_preempt(prio, rq_prio(inflight)))
> tasklet_hi_schedule(&engine->execlists.tasklet);
> +
> +unlock:
> + rcu_read_unlock();
> }
>
> static void __i915_schedule(struct i915_sched_node *node,
> --
> 2.24.0.rc2
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