We got report that setting cpuset.mems failed when the nodemask
contains a newly onlined memory node (not enumerated during boot)
for cgroup v2, while the binding succeeded for cgroup v1.

The root cause is, for cgroup v2, when a new memory node is onlined,
top_cpuset's 'mem_allowed' is not updated with the new nodemask of
memory nodes, and the following setting memory nodemask will fail,
if the nodemask contains a new node.

Fix it by updating top_cpuset.mems_allowed right after the
new memory node is onlined, just like v1.

Signed-off-by: Feng Tang <redacted>
---
Very likely I missed some details here, but it looks strange that
the top_cpuset.mem_allowed is not updatd even after we onlined
several memory nodes after boot.

 kernel/cgroup/cpuset.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 9390bfd9f1cd..b97caaf16374 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c

@@ -3314,8 +3314,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 	/* synchronize mems_allowed to N_MEMORY */
 	if (mems_updated) {
 		spin_lock_irq(&callback_lock);
-		if (!on_dfl)
-			top_cpuset.mems_allowed = new_mems;
+		top_cpuset.mems_allowed = new_mems;
 		top_cpuset.effective_mems = new_mems;
 		spin_unlock_irq(&callback_lock);
 		update_tasks_nodemask(&top_cpuset);

-- 
2.27.0