staging: vc04_services: don't increment service refcount when it's not needed

There are a few places where a service's reference count is incremented,
something quick is done, and the refcount is dropped. This can be made
a little simpler/faster by not grabbing a reference in these cases.
Signed-off-by: Marcelo Diop-Gonzalez <marcgonzalez@google.com>
Link: https://lore.kernel.org/r/ac6186ac888f1acf489b5b504efcba8b0d6a8b25.1581532523.git.marcgonzalez@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

@@ -2497,11 +2497,11 @@ vchiq_instance_get_use_count(struct vchiq_instance *instance)
 	int use_count = 0, i;
 
 	i = 0;
-	while ((service = next_service_by_instance(instance->state,
-		instance, &i))) {
+	rcu_read_lock();
+	while ((service = __next_service_by_instance(instance->state,
+						     instance, &i)))
 		use_count += service->service_use_count;
-		unlock_service(service);
-	}
+	rcu_read_unlock();
 	return use_count;
 }
 
@@ -2524,11 +2524,11 @@ vchiq_instance_set_trace(struct vchiq_instance *instance, int trace)
 	int i;
 
 	i = 0;
-	while ((service = next_service_by_instance(instance->state,
-		instance, &i))) {
+	rcu_read_lock();
+	while ((service = __next_service_by_instance(instance->state,
+						     instance, &i)))
 		service->trace = trace;
-		unlock_service(service);
-	}
+	rcu_read_unlock();
 	instance->trace = (trace != 0);
 }
 

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

@@ -222,28 +222,42 @@ find_closed_service_for_instance(struct vchiq_instance *instance,
 }
 
 struct vchiq_service *
-next_service_by_instance(struct vchiq_state *state, struct vchiq_instance *instance,
-			 int *pidx)
+__next_service_by_instance(struct vchiq_state *state,
+			   struct vchiq_instance *instance,
+			   int *pidx)
 {
 	struct vchiq_service *service = NULL;
 	int idx = *pidx;
 
-	rcu_read_lock();
 	while (idx < state->unused_service) {
 		struct vchiq_service *srv;
 
 		srv = rcu_dereference(state->services[idx++]);
 		if (srv && srv->srvstate != VCHIQ_SRVSTATE_FREE &&
-		    srv->instance == instance &&
-		    kref_get_unless_zero(&srv->ref_count)) {
-			service = rcu_pointer_handoff(srv);
+		    srv->instance == instance) {
+			service = srv;
 			break;
 		}
 	}
-	rcu_read_unlock();
 
 	*pidx = idx;
+	return service;
+}
 
+struct vchiq_service *
+next_service_by_instance(struct vchiq_state *state,
+			 struct vchiq_instance *instance,
+			 int *pidx)
+{
+	struct vchiq_service *service;
+
+	rcu_read_lock();
+	service = __next_service_by_instance(state, instance, pidx);
+	if (service && kref_get_unless_zero(&service->ref_count))
+		service = rcu_pointer_handoff(service);
+	else
+		service = NULL;
+	rcu_read_unlock();
 	return service;
 }
 
@@ -283,13 +297,13 @@ unlock_service(struct vchiq_service *service)
 int
 vchiq_get_client_id(unsigned int handle)
 {
-	struct vchiq_service *service = find_service_by_handle(handle);
+	struct vchiq_service *service;
 	int id;
 
+	rcu_read_lock();
+	service = handle_to_service(handle);
 	id = service ? service->client_id : 0;
-	if (service)
-		unlock_service(service);
-
+	rcu_read_unlock();
 	return id;
 }
 

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h

@@ -572,7 +572,13 @@ find_closed_service_for_instance(struct vchiq_instance *instance,
 	unsigned int handle);
 
 extern struct vchiq_service *
-next_service_by_instance(struct vchiq_state *state, struct vchiq_instance *instance,
+__next_service_by_instance(struct vchiq_state *state,
+			   struct vchiq_instance *instance,
+			   int *pidx);
+
+extern struct vchiq_service *
+next_service_by_instance(struct vchiq_state *state,
+			 struct vchiq_instance *instance,
 			 int *pidx);
 
 extern void