cgroup: Make cgroup_rstat_updated() ready for root cgroup usage

cgroup_rstat_updated() ensures that the cgroup's rstat is linked to the parent. If there's no parent, it never gets linked and the function ends up grabbing and releasing the cgroup_rstat_lock each time for no reason which can be expensive. This hasn't been a problem till now because nobody was calling the function for the root cgroup but rstat is gonna be exposed to controllers and use cases, so let's get ready. Make cgroup_rstat_updated() an no-op for the root cgroup. Signed-off-by: Tejun Heo <[email protected]>
xxmustafacooTR · Apr 22, 2023 · e3ba9c4 · e3ba9c4
1 parent 9e5fc06
commit e3ba9c4
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
@@ -27,6 +27,10 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
 	struct cgroup *parent;
 	unsigned long flags;
 
+	/* nothing to do for root */
+	if (!cgroup_parent(cgrp))
+		return;
+
 	/*
 	 * Paired with the one in cgroup_rstat_cpu_pop_upated().  Either we
 	 * see NULL updated_next or they see our updated stat.