sched/cpuset: Bring back cpuset_mutex
commit 111cd11b upstream. Turns out percpu_cpuset_rwsem - commit 1243dc51 ("cgroup/cpuset: Convert cpuset_mutex to percpu_rwsem") - wasn't such a brilliant idea, as it has been reported to cause slowdowns in workloads that need to change cpuset configuration frequently and it is also not implementing priority inheritance (which causes troubles with realtime workloads). Convert percpu_cpuset_rwsem back to regular cpuset_mutex. Also grab it only for SCHED_DEADLINE tasks (other policies don't care about stable cpusets anyway). Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Reviewed-by: Waiman Long <longman@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org> [ Conflict in kernel/cgroup/cpuset.c due to pulling new code/comments. Reject all new code. Remove BUG_ON() about rwsem that doesn't exist on mainline. ] Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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