Commit 5a0874c1 authored Nov 26, 2018 by Paul E. McKenney

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>

parent fb60e533

kernel/rcu/tree_exp.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

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