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It was discovered that isolated CPUs could sometimes be disturbed by kworkers processing kfree_rcu() works causing higher than expected latency. It is because the RCU core uses "system_wq" which doesn't have the WQ_UNBOUND flag to handle all its work items. Fix this violation of latency limits by using "system_unbound_wq" in the RCU core instead. This will ensure that those work items will not be run on CPUs marked as isolated. Beside the WQ_UNBOUND flag, the other major difference between system_wq and system_unbound_wq is their max_active count. The system_unbound_wq has a max_active of WQ_MAX_ACTIVE (512) while system_wq's max_active is WQ_DFL_ACTIVE (256) which is half of WQ_MAX_ACTIVE. Reported-by: Vratislav Bendel <vbendel@redhat.com> Closes: https://issues.redhat.com/browse/RHEL-50220 Signed-off-by: Waiman Long <longman@redhat.com> Reviewed-by: "Uladzislau Rezki (Sony)" <urezki@gmail.com> Tested-by: Breno Leitao <leitao@debian.org> Signed-off-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>