rcu: Remove preemption disabling from expedited CPU selection

It turns out that it is queue_delayed_work_on() rather than
queue_work_on() that has difficulties when used concurrently with
CPU-hotplug removal operations.  It is therefore unnecessary to protect
CPU identification and queue_work_on() with preempt_disable().

This commit therefore removes the preempt_disable() and preempt_enable()
from sync_rcu_exp_select_cpus(), which has the further benefit of reducing
the number of changes that must be maintained in the -rt patchset.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sebastian Siewior <bigeasy@linutronix.de>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index d882ca0cd01b569618cd068f1d16b4c0b940b995..763649d345d7c0665ae0117775dbb868dd20a1c3 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -448,7 +448,6 @@ static void sync_rcu_exp_select_cpus(void)
                        continue;
                }
                INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
-               preempt_disable();
                cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
                /* If all offline, queue the work on an unbound CPU. */
                if (unlikely(cpu > rnp->grphi - rnp->grplo))
@@ -456,7 +455,6 @@ static void sync_rcu_exp_select_cpus(void)
                else
                        cpu += rnp->grplo;
                queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
-               preempt_enable();
                rnp->exp_need_flush = true;
        }