[PATCH v7 0/9] cgroup/cpuset: Support multiple source/destination cpusets for cpuset_*attach()

[Waiman Long <longman@redhat.com>]

 v7:
  - Include the fix patch from Farhad Alemi to fix a div/0 crash that
    was part of the old patch 1.
  - Integrated v6 patch 7 into earlier patches.
  - Add a new "cgroup/cpuset: Prevent race between task attach and
    cpuset state change" patch to ensure that there will be no cpuset
    state change between cpuset_can_attach() and cpuset_attach() or
    cpuset_cancel_attach().
  - Break v6 patch 6 into 2 separate patches for supporting multiple
    source cpusets and multiple destination cpusets respectively and
    further simplify and streamline the code.

 v6:
  - Make guarantee_online_mems() to only return cs->effective_mems with v2
    in patch 1.
  - Remove obsolete commit description text from patch 3.
  - Add Reviewed-by tags.
  - In patch 6, add WARN_ON_ONCE() test in cpuset_can_attach() to
    confirm that cs != oldcs.

 v5:
  - Remove the WARN_ON() call as it can be triggered in a corner case.
  - Instead of passing an attach_cpus_updated and attach_mems_updated
    flags from cpuset_can_attach() to cpuset_attach(), re-evaluate the
    flags at the beginning of cpuset_attach() based on data in the source &
    destination cpusets in the singly linked lists to eliminate the
    Time-of-Check to Time-of-Use (TOCTOU) race condition & simplify the
    code changes.
  - Add back the dropped optimization in patch 5.

Sashiko AI review of another cpuset patch had found that cpuset_attach()
and cpuset_can_attach() can be passed a cgroup_taskset with tasks
migrating from one source cpuset to multiple destination cpusets and
vice versa.  Further testing of the cpuset code indicates that this is
indeed the case when the v2 cpuset controller is enabled or disabled.

Unfortunately, cpuset_attach() and cpuset_can_attach() still assume that
there will be one source and one destinaton cpuset which may result in
inocrrect behavior.

This patch series is created to fix this issue.

Patch 1 is a fix that fix a cgroup v2 div/0 crash due to bug in
cpuset_update_tasks_nodemask().

Patch 2 is to fix an inconsistency in the way node mask update is being
handled in cpuset_update_tasks_nodemask() and cpuset_attach() so that
they match each other.

Patch 3 makes any cpuset state change to wait for the completion of the
pending cpuset attach operation, if any.

Patches 4 and 5 are just preparatory patches to make the remaining
patches easier to review.

Patch 6 makes cpuset_attach_old_cs to track group leader for use by
cpuset_migrate_mm().

Patch 7 moves mpol_rebind_mm() and cpuset_migrate_mm() inside
cpuset_attach_task() to make CLONE_INTO_CGROUP flag of clone(2) works
more like moving task from one cpuset to another one, while also make
supporting multiple source and destination cpusets easier.

Patch 8 makes the necessary changes to enable the support of multiple
source cpusets by keeping all the source cpusets found during task
iterations in a singly linked lists.

Patch 9 enables the support of multiple destination cpusets during the
the enabling of cpuset v2 controller.

Farhad Alemi (1):
  cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed

Waiman Long (8):
  cgroup/cpuset: Fix node inconsistencies between
    cpuset_update_tasks_nodemask() and cpuset_attach()
  cgroup/cpuset: Prevent race between task attach and cpuset state
    change
  cgroup/cpuset: Add a cpuset_reserve_dl_bw() helper
  cgroup/cpuset: Expand the scope of cpuset_can_attach_check()
  cgroup/cpuset: Make cpuset_attach_old_cs track task group leaders
  cgroup/cpuset: Move mpol_rebind_mm/cpuset_migrate_mm() calls inside
    cpuset_attach_task()
  cgroup/cpuset: Support multiple source cpusets for cpuset_*attach()
  cgroup/cpuset: Support multiple destination cpusets for
    cpuset_*attach()

 kernel/cgroup/cpuset-internal.h |   2 +
 kernel/cgroup/cpuset.c          | 400 ++++++++++++++++++++++----------
 2 files changed, 277 insertions(+), 125 deletions(-)

-- 
2.54.0