[PATCH v2 5/6] cgroup/cpuset: Release CPUs when type-change validation fails

[Guopeng Zhang <guopeng.zhang@linux.dev>]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

When housekeeping validation fails during a root-to-isolated or
isolated-to-root change, update_prstate() records the requested partition
type as invalid but leaves its effective_xcpus allocated. Those CPUs are
not returned to the partition which owns the invalidated subtree.

This can be reproduced on a cgroup v2 system booted with
isolcpus=domain,15:

    cd /sys/fs/cgroup
    echo +cpuset > cgroup.subtree_control
    mkdir type-fail-repro
    echo 15 > type-fail-repro/cpuset.cpus
    echo isolated > type-fail-repro/cpuset.cpus.partition
    echo root > type-fail-repro/cpuset.cpus.partition
    cat type-fail-repro/cpuset.cpus.partition
    cat cpuset.cpus.effective

The requested root type is recorded as invalid, but CPU 15 remains
unavailable to the top cpuset.

Use the common partition-disable path when housekeeping validation fails.
Disable a remote partition with remote_partition_disable(); for a local
partition, return effective_xcpus to its parent. If that return would
consume the last housekeeping CPU, invalidate the outermost isolated
ancestor instead.

Fixes: 103b08709e8a ("cgroup/cpuset: Fail if isolated and nohz_full don't leave any housekeeping")
Fixes: b1034a690129 ("cgroup/cpuset: Ensure domain isolated CPUs stay in root or isolated partition")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 kernel/cgroup/cpuset.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 32a37d624c6b..fefc0afa93ec 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2990,6 +2990,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	struct cpuset *parent = parent_cs(cs);
 	struct cpuset *invalidated = NULL;
 	struct tmpmasks tmpmask;
+	bool disable_partition = false;
 	bool isolcpus_updated = false;
 
 	if (old_prs == new_prs)
@@ -3052,15 +3053,21 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 						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
+			disable_partition = true;
+		} else {
 			isolcpus_updated = true;
+		}
 	} else {
 		/*
 		 * Switching back to member is always allowed even if it
 		 * disables child partitions.
 		 */
+		disable_partition = true;
+	}
+
+	if (disable_partition) {
 		if (old_prs == PRS_ROOT &&
 		    parent->partition_root_state == PRS_ISOLATED &&
 		    !isolated_cpus_can_update(cs->effective_xcpus, NULL))
-- 
2.43.0