[PATCH v5 0/6] cgroup/cpuset: Fix partition related locking issues

[Waiman Long <longman@redhat.com>]

 v5:
  - Reapply on top of the latest upstream linux tree.
  - Add a new fix patch for a cpuset bug found during testing.
  - Add a patch to not update isolated_cpus when calling from CPU
    hotplug. As a result, CPU hotplug won't need to call
    housekeeping_update() at all and the corresponding wq deferral
    patch is dropped.

 v4:
  - https://lore.kernel.org/lkml/20260206203712.1989610-1-longman@redhat.com/

After booting the latest cgroup for-next debug kernel with the latest
cgroup changes as well as Federic's "cpuset/isolation: Honour kthreads
preferred affinity" patch series [1] merged on top and running the
test-cpuset-prs.sh test, a circular locking dependency lockdep splat
was reported. See patch 5 for details.

To fix this issue, the cpuset code is modified to not doing any
update to isolated_cpus when calling from CPU hotplug. In addition,
the housekeeping_update() call, when needed, is deferred to task_work
so that it can be called without holding a cpus_read_lock. A new top
level cpuset_top_mutex is also added to have more exclusion control.

With these changes in place, the cpuset test ran to completion with no
failure and no lockdep splat.

[1] https://lore.kernel.org/lkml/20260125224541.50226-1-frederic@kernel.org/

Waiman Long (6):
  cgroup/cpuset: Fix incorrect change to effective_xcpus in
    partition_xcpus_del()
  cgroup/cpuset: Clarify exclusion rules for cpuset internal variables
  cgroup/cpuset: Set isolated_cpus_updating only if isolated_cpus is
    changed
  cgroup/cpuset: Don't update isolated_cpus from CPU hotplug
  cgroup/cpuset: Call housekeeping_update() without holding
    cpus_read_lock
  cgroup/cpuset: Eliminate some duplicated rebuild_sched_domains() calls

 kernel/cgroup/cpuset.c                        | 313 ++++++++++++++----
 kernel/sched/isolation.c                      |   4 +-
 kernel/time/timer_migration.c                 |   4 +-
 .../selftests/cgroup/test_cpuset_prs.sh       |  21 +-
 4 files changed, 259 insertions(+), 83 deletions(-)

-- 
2.52.0