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Hui Peng 31c88350b7 cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict 
When a remote partition is created underneath an existing local partition
via a non-partition (PRS_MEMBER) intermediate cgroup, update_prstate() sees
parent->partition_root_state == PRS_MEMBER and calls
remote_partition_enable().

Commit 86888c7bd1 ("cgroup/cpuset: Add warnings to catch inconsistency
in exclusive CPUs") replaced the cpumask_intersects(tmp->new_cpus,
subpartitions_cpus) error check in remote_partition_enable() with
WARN_ON_ONCE(). As a result, remote_partition_enable() emits a warning
and proceeds to enable the remote partition on CPUs that are already
owned by the ancestor local partition in subpartitions_cpus.

This can be reproduced on Linux 7.3.0-rc3 with:

  mkdir -p /tmp/cg1
  mount -t cgroup2 none /tmp/cg1
  echo "+cpuset" > /tmp/cg1/cgroup.subtree_control

  mkdir /tmp/cg1/A
  echo 1 > /tmp/cg1/A/cpuset.cpus
  echo 1 > /tmp/cg1/A/cpuset.cpus.exclusive
  echo root > /tmp/cg1/A/cpuset.cpus.partition
  echo "+cpuset" > /tmp/cg1/A/cgroup.subtree_control

  mkdir /tmp/cg1/A/B
  echo 1 > /tmp/cg1/A/B/cpuset.cpus
  echo 1 > /tmp/cg1/A/B/cpuset.cpus.exclusive
  echo "+cpuset" > /tmp/cg1/A/B/cgroup.subtree_control

  mkdir /tmp/cg1/A/B/D
  echo 1 > /tmp/cg1/A/B/D/cpuset.cpus
  echo 1 > /tmp/cg1/A/B/D/cpuset.cpus.exclusive
  echo root > /tmp/cg1/A/B/D/cpuset.cpus.partition

which triggers:

  WARNING: kernel/cgroup/cpuset.c:1594 at remote_partition_enable+0x1c1/0x300

and leaves both /tmp/cg1/A and /tmp/cg1/A/B/D as active root partitions
claiming exclusive CPU 1.

Fix this by returning PERR_NOCPUS when tmp->new_cpus intersects
subpartitions_cpus in remote_partition_enable(), matching the error code
used by remote_cpus_update() for the same subpartitions_cpus conflict, and
add a regression test case to
tools/testing/selftests/cgroup/test_cpuset_prs.sh.

Tested in QEMU on Linux 7.3.0-rc3 using the reproducer above and
tools/testing/selftests/cgroup/test_cpuset_prs.sh.

Fixes: 86888c7bd1 ("cgroup/cpuset: Add warnings to catch inconsistency in exclusive CPUs")
Suggested-by: Guopeng Zhang <guopeng.zhang@linux.dev>
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
2026-09-26 08:07:26 -10:00
..
crypto/chacha20-s390 crypto: drbg - Fold include/crypto/drbg.h into crypto/drbg.c 2026-05-07 16:09:59 +08:00
cxl Merge branch 'for-7.2/cxl-type2-attach-region' into cxl-for-next 2026-06-12 13:47:53 -07:00
fault-injection
ktest ktest: Add logfile to failure directory 2026-04-20 15:23:13 -04:00
kunit kunit:tool: Don't write to stdout when it should be disabled 2026-06-07 20:10:30 -06:00
memblock liveupdate: updates for 7.2-rc1 2026-06-21 09:46:14 -07:00
nvdimm
radix-tree MAINTAINERS: update Liam's email address 2026-04-27 05:54:25 -07:00
rbtree
scatterlist
selftests cgroup/cpuset: Return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict 2026-09-26 08:07:26 -10:00
shared mm/slab: improve kmem_cache_alloc_bulk 2026-06-03 18:20:43 +02:00
vma mm/vma: eliminate mmap_action->error_hook, introduce error_override 2026-06-04 14:45:00 -07:00
vsock vsock/test: add MSG_PEEK after partial recv test 2026-04-16 19:34:22 -07:00