drm/i915: Add reference count to request structure

The plan is to use request structures everywhere that seqno values were
previously used. This means saving pointers to structures in places that used to
be simple integers. In turn, that means that the target structure now needs much
more stringent lifetime tracking. That is, it must not be freed while some other
random object still holds a pointer to it.

To achieve this tracking, a reference count needs to be added. Whenever a
pointer to the structure is saved away, the count must be incremented and the
free must only occur when all references have been released.

For: VIZ-4377
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Thomas Daniel <Thomas.Daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2569,21 +2569,30 @@ static void i915_set_reset_status(struct drm_i915_private *dev_priv,
 
 static void i915_gem_free_request(struct drm_i915_gem_request *request)
 {
-	struct intel_context *ctx = request->ctx;
-
 	list_del(&request->list);
 	i915_gem_request_remove_from_client(request);
 
+	i915_gem_request_unreference(request);
+}
+
+void i915_gem_request_free(struct kref *req_ref)
+{
+	struct drm_i915_gem_request *req = container_of(req_ref,
+						 typeof(*req), ref);
+	struct intel_context *ctx = req->ctx;
+
 	if (ctx) {
 		if (i915.enable_execlists) {
-			struct intel_engine_cs *ring = request->ring;
+			struct intel_engine_cs *ring = req->ring;
 
 			if (ctx != ring->default_context)
 				intel_lr_context_unpin(ring, ctx);
 		}
+
 		i915_gem_context_unreference(ctx);
 	}
-	kfree(request);
+
+	kfree(req);
 }
 
 struct drm_i915_gem_request *
@@ -2671,8 +2680,7 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
 	}
 
 	/* These may not have been flush before the reset, do so now */
-	kfree(ring->preallocated_lazy_request);
-	ring->preallocated_lazy_request = NULL;
+	i915_gem_request_assign(&ring->preallocated_lazy_request, NULL);
 	ring->outstanding_lazy_seqno = 0;
 }