cgroup/cpuset: Enforce at most one rebuild_sched_domains_locked() call per operation

Since commit ff0ce721ec21 ("cgroup/cpuset: Eliminate unncessary
sched domains rebuilds in hotplug"), there is only one
rebuild_sched_domains_locked() call per hotplug operation. However,
writing to the various cpuset control files may still casue more than
one rebuild_sched_domains_locked() call to happen in some cases.

Juri had found that two rebuild_sched_domains_locked() calls in
update_prstate(), one from update_cpumasks_hier() and another one from
update_partition_sd_lb() could cause cpuset partition to be created
with null total_bw for DL tasks. IOW, DL tasks may not be scheduled
correctly in such a partition.

A sample command sequence that can reproduce null total_bw is as
follows.

  # echo Y >/sys/kernel/debug/sched/verbose
  # echo +cpuset >/sys/fs/cgroup/cgroup.subtree_control
  # mkdir /sys/fs/cgroup/test
  # echo 0-7 > /sys/fs/cgroup/test/cpuset.cpus
  # echo 6-7 > /sys/fs/cgroup/test/cpuset.cpus.exclusive
  # echo root >/sys/fs/cgroup/test/cpuset.cpus.partition

Fix this double rebuild_sched_domains_locked() calls problem
by replacing existing calls with cpuset_force_rebuild() except
the rebuild_sched_domains_cpuslocked() call at the end of
cpuset_handle_hotplug(). Checking of the force_sd_rebuild flag is
now done at the end of cpuset_write_resmask() and update_prstate()
to determine if rebuild_sched_domains_locked() should be called or not.

The cpuset v1 code can still call rebuild_sched_domains_locked()
directly as double rebuild_sched_domains_locked() calls is not possible.

Reported-by: Juri Lelli <juri.lelli@redhat.com>
Closes: https://lore.kernel.org/lkml/ZyuUcJDPBln1BK1Y@jlelli-thinkpadt14gen4.remote.csb/
Signed-off-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions