rcu: Check for NOCB CPUs and empty lists earlier in CB migration (95335c03) · Commits · 戴 / test

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:

Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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);

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