[RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated partitions

[Waiman Long]

This patch series is based on the RFC patch from Frederic [1]. Instead
of offering RCU_NOCB as a separate option, it is now lumped into a
root-only cpuset.cpus.isolation_full flag that will enable all the
additional CPU isolation capabilities available for isolated partitions
if set. RCU_NOCB is just the first one to this party. Additional dynamic
CPU isolation capabilities will be added in the future.

The first 2 patches are adopted from Federic with minor twists to fix
merge conflicts and compilation issue. The rests are for implementing
the new cpuset.cpus.isolation_full interface which is essentially a flag
to globally enable or disable full CPU isolation on isolated partitions.
On read, it also shows the CPU isolation capabilities that are currently
enabled. RCU_NOCB requires that the rcu_nocbs option be present in
the kernel boot command line. Without that, the rcu_nocb functionality
cannot be enabled even if the isolation_full flag is set. So we allow
users to check the isolation_full file to verify that if the desired
CPU isolation capability is enabled or not.

Only sanity checking has been done so far. More testing, especially on
the RCU side, will be needed.

[1] https://lore.kernel.org/lkml/20220525221055.1152307-1-frederic@xxxxxxxxxx/

Frederic Weisbecker (2):
  rcu/nocb: Pass a cpumask instead of a single CPU to offload/deoffload
  rcu/nocb: Prepare to change nocb cpumask from CPU-hotplug protected
    cpuset caller

Waiman Long (6):
  rcu/no_cb: Add rcu_nocb_enabled() to expose the rcu_nocb state
  cgroup/cpuset: Better tracking of addition/deletion of isolated CPUs
  cgroup/cpuset: Add cpuset.cpus.isolation_full
  cgroup/cpuset: Enable dynamic rcu_nocb mode on isolated CPUs
  cgroup/cpuset: Document the new cpuset.cpus.isolation_full control
    file
  cgroup/cpuset: Update test_cpuset_prs.sh to handle
    cpuset.cpus.isolation_full

 Documentation/admin-guide/cgroup-v2.rst       |  24 ++
 include/linux/rcupdate.h                      |  15 +-
 kernel/cgroup/cpuset.c                        | 237 ++++++++++++++----
 kernel/rcu/rcutorture.c                       |   6 +-
 kernel/rcu/tree_nocb.h                        | 118 ++++++---
 .../selftests/cgroup/test_cpuset_prs.sh       |  23 +-
 6 files changed, 337 insertions(+), 86 deletions(-)

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2.39.3