[PATCH-next v2 07/10] cgroup/cpuset: Make sure compute_partition_effective_cpumask() is only called for valid partition

[Waiman Long <longman@redhat.com>]

With visual inspection to make sure that
compute_partition_effective_cpumask() is only called for valid partition
root, it was found that the function can be called for an invalidated
partition near the end of cpuset_hotplug_update_tasks(). When partcmd is
set, update_parent_effective_cpumask() is called to either invalidate a
valid partition or with partcmd_update to check if an invalid partition
can be switched back to valid. In both cases, cpuset_force_rebuild()
should be invoked. However, compute_partition_effective_cpumask()
should only be called when an invalid partition is switched back to
valid. When a partition is invalidated, compute_effective_cpumask()
should be called instead.

Also add a WARN_ON_ONCE() in compute_partition_effective_cpumask() to
ensure that a valid partition root is passed in.

Fixes: 72c6303acfa1 ("cgroup/cpuset: Take isolated CPUs out of workqueue unbound cpumask")
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index d995f1ec5259..2c3a148fa40b 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2116,6 +2116,8 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
 	struct cpuset *child;
 	bool populated = partition_is_populated(cs, NULL);
 
+	WARN_ON_ONCE(!is_partition_valid(cs));
+
 	/*
 	 * Check child partition roots to see if they should be
 	 * invalidated when
@@ -4023,9 +4025,12 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
 
 	if (partcmd >= 0) {
 		update_parent_effective_cpumask(cs, partcmd, NULL, tmp);
-		if ((partcmd == partcmd_invalidate) || is_partition_valid(cs)) {
+		if (is_partition_valid(cs)) {
 			compute_partition_effective_cpumask(cs, &new_cpus);
 			cpuset_force_rebuild();
+		} else if (partcmd == partcmd_invalidate) {
+			compute_effective_cpumask(&new_cpus, cs, parent);
+			cpuset_force_rebuild();
 		}
 	}
 
-- 
2.56.0