[PATCH 08/17] cgroup/cpuset: Release CPUs when a type change is rejected

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>

When a housekeeping check rejects a root-to-isolated or isolated-to-root
change, update_prstate() marks the partition invalid but leaves its
effective_xcpus allocated. Those CPUs remain missing from the partition
which owns the invalidated subtree.

Disable a rejected remote partition with remote_partition_disable().
For a local partition, return effective_xcpus to its parent before
recording the invalid state. Use the complete mask because descendants
are invalidated along with the parent and their CPUs return at the same
time.

Fixes: 103b08709e8a ("cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping")
Signed-off-by: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>
---
 kernel/cgroup/cpuset.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 853942c1afeb..a616012927be 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3020,10 +3020,21 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 		compute_partition_owned_cpumask(cs, tmpmask.new_cpus);
 		if (((new_prs == PRS_ISOLATED) &&
 		     !isolated_cpus_can_update(tmpmask.new_cpus, NULL)) ||
-		    prstate_housekeeping_conflict(new_prs, tmpmask.new_cpus))
+		    prstate_housekeeping_conflict(new_prs, tmpmask.new_cpus)) {
 			err = PERR_HKEEPING;
-		else
+			if (is_remote_partition(cs)) {
+				WRITE_ONCE(cs->prs_err, err);
+				remote_partition_disable(cs, &tmpmask);
+			} else {
+				spin_lock_irq(&callback_lock);
+				partition_xcpus_del(old_prs, parent, cs->effective_xcpus);
+				spin_unlock_irq(&callback_lock);
+				cpuset_update_tasks_cpumask(parent, tmpmask.new_cpus);
+				update_sibling_cpumasks(parent, cs, &tmpmask);
+			}
+		} else {
 			isolcpus_updated = true;
+		}
 	} else {
 		/*
 		 * Switching back to member is always allowed even if it
-- 
2.43.0