[PATCH v2 0/3] cgroup/cpuset: Keep the top scheduling domain populated

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

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

Boot-isolated CPUs stay in top_cpuset.effective_cpus, but are excluded
from its scheduling domain. Allocating all boot domain housekeeping CPUs
to partitions can therefore leave the top scheduling domain empty even
though effective_cpus is nonempty, leading to warnings and an OOPS in
build_perf_domains(). CPU hotplug can reach the same state.

The patches are ordered as follows:

  1. Check local and remote partition creation and CPU mask updates.
  2. Check the hotplug paths without crediting CPUs that remain allocated
     to child partitions, and invalidate local or remote partitions as
     needed to restore an active boot domain housekeeping CPU.
  3. Release an isolated child's CPUs when its parent is already invalid.

Changes since v1:
  Rework the fix following Ridong's suggestion and add test cases.
  Add patch 2 for CPU hotplug and patch 3 for isolated CPU cleanup
  when the parent partition becomes invalid.

  v1: https://lore.kernel.org/all/20261104071600.474587-1-guopeng.zhang@linux.dev/

Guopeng Zhang (3):
  cgroup/cpuset: Reject updates that empty the top sched domain
  cgroup/cpuset: Keep the top sched domain non-empty on CPU hotplug
  cgroup/cpuset: Release isolated CPUs when the parent is invalid

 kernel/cgroup/cpuset.c                        | 59 ++++++++++++++++++-
 .../selftests/cgroup/test_cpuset_prs.sh       | 55 +++++++++++++++++
 2 files changed, 111 insertions(+), 3 deletions(-)

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2.43.0