drm/i915/execlists: Lock the request while validating it during promotion

Since the request is already on the HW as we perform its validation, it
and even its subsequent barrier may be concurrently retired before we
process the assertions. If it is retired already and so off the HW, our
assertions become void and we need to ignore them.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=112363Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191121103546.146487-1-chris@chris-wilson.co.uk

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

@@ -1291,38 +1291,53 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
 	}
 
 	for (port = execlists->pending; (rq = *port); port++) {
+		unsigned long flags;
+		bool ok = true;
+
 		if (ce == rq->hw_context) {
 			GEM_TRACE_ERR("Dup context:%llx in pending[%zd]\n",
 				      ce->timeline->fence_context,
 				      port - execlists->pending);
 			return false;
 		}
-
 		ce = rq->hw_context;
+
+		/* Hold tightly onto the lock to prevent concurrent retires! */
+		spin_lock_irqsave_nested(&rq->lock, flags,
+					 SINGLE_DEPTH_NESTING);
+
 		if (i915_request_completed(rq))
-			continue;
+			goto unlock;
 
 		if (i915_active_is_idle(&ce->active) &&
 		    !i915_gem_context_is_kernel(ce->gem_context)) {
 			GEM_TRACE_ERR("Inactive context:%llx in pending[%zd]\n",
 				      ce->timeline->fence_context,
 				      port - execlists->pending);
-			return false;
+			ok = false;
+			goto unlock;
 		}
 
 		if (!i915_vma_is_pinned(ce->state)) {
 			GEM_TRACE_ERR("Unpinned context:%llx in pending[%zd]\n",
 				      ce->timeline->fence_context,
 				      port - execlists->pending);
-			return false;
+			ok = false;
+			goto unlock;
 		}
 
 		if (!i915_vma_is_pinned(ce->ring->vma)) {
 			GEM_TRACE_ERR("Unpinned ring:%llx in pending[%zd]\n",
 				      ce->timeline->fence_context,
 				      port - execlists->pending);
-			return false;
+			ok = false;
+			goto unlock;
 		}
+
+unlock:
+		spin_unlock_irqrestore(&rq->lock, flags);
+		if (!ok)
+			return false;
 	}
 
 	return ce;