Merge: blk-cgroup: don't update io stat for root cgroup

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/2021

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2167245

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Approved-by: Waiman Long <longman@redhat.com>
Approved-by: Xiao Ni <xni@redhat.com>

Signed-off-by: Herton R. Krzesinski <herton@redhat.com>

Author: Herton R. Krzesinski

block/blk-cgroup.c

@@ -1996,6 +1996,10 @@ void blk_cgroup_bio_start(struct bio *bio)
 	struct blkg_iostat_set *bis;
 	unsigned long flags;
 
+	/* Root-level stats are sourced from system-wide IO stats */
+	if (!cgroup_parent(blkcg->css.cgroup))
+		return;
+
 	cpu = get_cpu();
 	bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu);
 	flags = u64_stats_update_begin_irqsave(&bis->sync);