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Commit 9b683874 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Stop disabling CPU hotplug in synchronize_rcu_expedited() 



The fact that tasks could be migrated from leaf to root rcu_node
structures meant that synchronize_rcu_expedited() had to disable
CPU hotplug.  However, tasks now stay put, so this commit removes the
CPU-hotplug disabling from synchronize_rcu_expedited().

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 13bd6494

kernel/rcu/tree_plugin.h

+2 −23
Original line number Diff line number Diff line
@@ -727,20 +727,6 @@ void synchronize_rcu_expedited(void) 
	snap = READ_ONCE(sync_rcu_preempt_exp_count) + 1;

	smp_mb(); /* Above access cannot bleed into critical section. */



	/*

	 * Block CPU-hotplug operations.  This means that any CPU-hotplug

	 * operation that finds an rcu_node structure with tasks in the

	 * process of being boosted will know that all tasks blocking

	 * this expedited grace period will already be in the process of

	 * being boosted.  This simplifies the process of moving tasks

	 * from leaf to root rcu_node structures.

	 */

	if (!try_get_online_cpus()) {

		/* CPU-hotplug operation in flight, fall back to normal GP. */

		wait_rcu_gp(call_rcu);

		return;

	}



	/*

	 * Acquire lock, falling back to synchronize_rcu() if too many

	 * lock-acquisition failures.  Of course, if someone does the
@@ -748,22 +734,17 @@ void synchronize_rcu_expedited(void) 
	 */

	while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {

		if (ULONG_CMP_LT(snap,

		    READ_ONCE(sync_rcu_preempt_exp_count))) {

			put_online_cpus();

		    READ_ONCE(sync_rcu_preempt_exp_count)))

			goto mb_ret; /* Others did our work for us. */

		}

		if (trycount++ < 10) {

			udelay(trycount * num_online_cpus());

		} else {

			put_online_cpus();

			wait_rcu_gp(call_rcu);

			return;

		}

	}

	if (ULONG_CMP_LT(snap, READ_ONCE(sync_rcu_preempt_exp_count))) {

		put_online_cpus();

	if (ULONG_CMP_LT(snap, READ_ONCE(sync_rcu_preempt_exp_count)))

		goto unlock_mb_ret; /* Others did our work for us. */

	}



	/* force all RCU readers onto ->blkd_tasks lists. */

	synchronize_sched_expedited();
@@ -779,8 +760,6 @@ void synchronize_rcu_expedited(void) 
	rcu_for_each_leaf_node(rsp, rnp)

		sync_rcu_preempt_exp_init2(rsp, rnp);



	put_online_cpus();



	/* Wait for snapshotted ->blkd_tasks lists to drain. */

	rnp = rcu_get_root(rsp);

	wait_event(sync_rcu_preempt_exp_wq,