drm/i915: Protect request peeking with RCU

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")
Fixes: 13ed13a4dcbf ("drm/i915: Don't set queue_priority_hint if we don't kick the submission")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191104090158.2959-2-chris@chris-wilson.co.uk
(cherry picked from commit 7d148635253328dda7cfe55d57e3c828e9564427)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/i915_scheduler.c b/drivers/gpu/drm/i915/i915_scheduler.c
index d2edb52..010d67f 100644 (file)
--- 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,