On Thu, 2018-08-09 at 12:56 -0700, Tejun Heo wrote:

Hello,
=20
On Thu, Aug 09, 2018 at 07:53:36AM -0700, Bart Van Assche wrote:

quoted

+/**
+ * blkg_lookup - look up blkg for the specified reque=

st queue

quoted

+ * @q: request_queue of interest
+ *
+ * Lookup blkg for @q at the root level. See also blk=

g_lookup().

quoted

+ */
+static inline struct blkcg_gq *blkg_root_look=

up(struct request_queue *q)

quoted

+{
+	struct blkcg_gq *blkg;
+
+	rcu_read_lock();
+	blkg = blkg_lookup(&blkcg_root, q);
+	rcu_read_unlock();
+
+	return blkg;
+}

=20
So, root blkg is always available as long as the request_queue is
alive.  Sth like the following would be simpler?
=20
static inline struct blkcg_gq *blk_queue_root_blk=

g(struct request_queue *q)

{
	return q->root_blkg;
}

That would not only be simpler, it would also avoid that blk_queue_=
root_blkg()
returns NULL if bypass mode is enabled and the request queue is still assoc=
iated
with the block cgroup controller. How do you want to proceed with this chan=
ge?

Bart.