[PATCH v2 2/3] cgroup/cpuset: Recompute effective cpumask in update_cpumasks_hier() after calling update_parent_effective_cpumask()

[Waiman Long]

It is reported by sashiko that calling update_parent_effective_cpumask()
may clobber tmp->new_cpus when update_sibling_cpumasks() needs to be
called due to possible change in the parent's effective_cpus value.
Therefore the new effective cpumask has to be recomputed after calling
update_parent_effective_cpumask() to get a correct value back into
tmp->new_cpus.

Fixes: f0af1bfc27b5 ("cgroup/cpuset: Relax constraints to partition & cpus changes")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/cgroup/cpuset.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 39c81a0a8ab9..ed014ecb770c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2359,12 +2359,12 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 			update_parent_effective_cpumask(cp, partcmd_update, NULL, tmp);
 			/*
 			 * Capture current partition_root_state as it may have
-			 * changed. Recompute effective cpumask if changed.
+			 * changed. Always recompute effective cpumask as tmp->new_cpus
+			 * may be clobbered when update_sibling_cpumasks() is called
+			 * within update_parent_effective_cpumask().
 			 */
 			new_prs = cp->partition_root_state;
-			if (new_prs != old_prs) {
-				compute_effective_cpumask(tmp->new_cpus, cp, parent);
-			}
+			compute_effective_cpumask(tmp->new_cpus, cp, parent);
 		}
 
 		spin_lock_irq(&callback_lock);
-- 
2.56.0