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

[Waiman Long]

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 <long...@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