[PATCH-cgroup 4/5] cgroup/cpuset: Check for partition roots with overlapping CPUs

[Waiman Long <longman@redhat.com>]

With the previous commit that eliminates the overlapping partition
root corner cases in the hotplug code, the partition roots passed down
to generate_sched_domains() should not have overlapping CPUs. Enable
overlapping cpuset check for v2 and warn if that happens.

This patch also has the benefit of increasing test coverage of the new
Union-Find cpuset merging code to cgroup v2.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e070e391d7a8..e34fd6108b06 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1127,25 +1127,27 @@ static int generate_sched_domains(cpumask_var_t **domains,
 	if (root_load_balance && (csn == 1))
 		goto single_root_domain;
 
-	if (!cgrpv2) {
-		for (i = 0; i < csn; i++)
-			uf_node_init(&csa[i]->node);
-
-		/* Merge overlapping cpusets */
-		for (i = 0; i < csn; i++) {
-			for (j = i + 1; j < csn; j++) {
-				if (cpusets_overlap(csa[i], csa[j]))
-					uf_union(&csa[i]->node, &csa[j]->node);
+	for (i = 0; i < csn; i++)
+		uf_node_init(&csa[i]->node);
+
+	/* Merge overlapping cpusets */
+	for (i = 0; i < csn; i++) {
+		for (j = i + 1; j < csn; j++) {
+			if (cpusets_overlap(csa[i], csa[j])) {
+				/*
+				 * Cgroup v2 shouldn't pass down overlapping
+				 * partition root cpusets.
+				 */
+				WARN_ON_ONCE(cgrpv2);
+				uf_union(&csa[i]->node, &csa[j]->node);
 			}
 		}
+	}
 
-		/* Count the total number of domains */
-		for (i = 0; i < csn; i++) {
-			if (uf_find(&csa[i]->node) == &csa[i]->node)
-				ndoms++;
-		}
-	} else {
-		ndoms = csn;
+	/* Count the total number of domains */
+	for (i = 0; i < csn; i++) {
+		if (uf_find(&csa[i]->node) == &csa[i]->node)
+			ndoms++;
 	}
 
 	/*
-- 
2.43.5