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Commit 95335c03 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Check for NOCB CPUs and empty lists earlier in CB migration 



The current CPU-hotplug RCU-callback-migration code checks
for the source (newly offlined) CPU being a NOCBs CPU down in
rcu_send_cbs_to_orphanage().  This commit simplifies callback migration a
bit by moving this check up to rcu_migrate_callbacks().  This commit also
adds a check for the source CPU having no callbacks, which eases analysis
of the rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() functions.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent c47e067a

kernel/rcu/tree.c

+3 −4
Original line number Diff line number Diff line
@@ -3862,10 +3862,6 @@ rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp, 
{

	lockdep_assert_held(&rsp->orphan_lock);



	/* No-CBs CPUs do not have orphanable callbacks. */

	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu))

		return;



	/*

	 * Orphan the callbacks.  First adjust the counts.  This is safe

	 * because _rcu_barrier() excludes CPU-hotplug operations, so it
@@ -3935,6 +3931,9 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp) 
	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);

	struct rcu_node *rnp = rdp->mynode;  /* Outgoing CPU's rdp & rnp. */



	if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))

		return;  /* No callbacks to migrate. */



	raw_spin_lock_irqsave(&rsp->orphan_lock, flags);

	rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);

	rcu_adopt_orphan_cbs(rsp, flags);