[PATCH v3 6/7] 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/isolated type change,
update_prstate() marks the requested state invalid without running the
partition-disable path. The failed partition's effective_xcpus may be
cleared, but its CPUs remain unavailable 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 state is recorded as invalid, but CPU 15 remains
unavailable to the top cpuset.

Run the common partition-disable path when housekeeping validation fails.
Disable remote partitions with remote_partition_disable() and return local
partition CPUs to their parent. If that 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 | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 19efa62bb694..30d9ea5f3859 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3042,6 +3042,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 	struct cpuset *invalidated = NULL;
 	struct cpumask *isolcpus_update_cpus = cs->effective_xcpus;
 	struct tmpmasks tmpmask;
+	bool disable_partition = false;
 	bool isolcpus_updated = false;
 
 	if (old_prs == new_prs)
@@ -3107,6 +3108,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 		     !isolated_cpus_can_update(tmpmask.new_cpus, NULL)) ||
 		    prstate_housekeeping_conflict(new_prs, tmpmask.new_cpus)) {
 			err = PERR_HKEEPING;
+			disable_partition = true;
 		} else {
 			/*
 			 * Only directly owned CPUs change isolation state for a
@@ -3122,6 +3124,10 @@ static int update_prstate(struct cpuset *cs, int new_prs)
 		 * parent would consume the last housekeeping CPU, invalidate
 		 * the outermost isolated ancestor and return its CPUs instead.
 		 */
+		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