drm/i915/execlists: Keep virtual context alive until after we kick

The call to kick_siblings() dereferences the rq->context, so we should
not drop our local reference until afterwards!

v2: Stick to setting ce.inflight=NULL before kicking as this is what the
other threads will check to see if the context is ready for takeover.

Fixes: 22b7a426 ("drm/i915/execlists: Preempt-to-busy")
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: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621080729.2652-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -557,9 +557,6 @@ execlists_schedule_out(struct i915_request *rq)
 		intel_engine_context_out(ce->inflight);
 		execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_OUT);
 
-		ce->inflight = NULL;
-		intel_context_put(ce);
-
 		/*
 		 * If this is part of a virtual engine, its next request may
 		 * have been blocked waiting for access to the active context.
@@ -569,8 +566,11 @@ execlists_schedule_out(struct i915_request *rq)
 		 * request before the tasklet runs and do not need to rebuild
 		 * each virtual tree and kick everyone again.
 		 */
+		ce->inflight = NULL;
 		if (rq->engine != ce->engine)
 			kick_siblings(rq, ce);
+
+		intel_context_put(ce);
 	}
 
 	i915_request_put(rq);