Commit 2cb1f6e9 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

rcu: Conditionally build CPU-hotplug teardown callbacks 



Among the three CPU-hotplug teardown RCU callbacks, two of them early
exit if CONFIG_HOTPLUG_CPU=n, and one is left unchanged. In any case
all of them have an implementation when CONFIG_HOTPLUG_CPU=n.

Align instead with the common way to deal with CPU-hotplug teardown
callbacks and provide a proper stub when they are not supported.

Reviewed-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
parent c964c1f5

include/linux/rcutree.h

+9 −2
Original line number Diff line number Diff line
@@ -110,9 +110,16 @@ void rcu_all_qs(void); 
/* RCUtree hotplug events */

int rcutree_prepare_cpu(unsigned int cpu);

int rcutree_online_cpu(unsigned int cpu);

int rcutree_offline_cpu(unsigned int cpu);

void rcu_cpu_starting(unsigned int cpu);



#ifdef CONFIG_HOTPLUG_CPU

int rcutree_dead_cpu(unsigned int cpu);

int rcutree_dying_cpu(unsigned int cpu);

void rcu_cpu_starting(unsigned int cpu);

int rcutree_offline_cpu(unsigned int cpu);

#else

#define rcutree_dead_cpu NULL

#define rcutree_dying_cpu NULL

#define rcutree_offline_cpu NULL

#endif



#endif /* __LINUX_RCUTREE_H */

kernel/rcu/tree.c

+54 −60
Original line number Diff line number Diff line
@@ -4237,25 +4237,6 @@ static bool rcu_init_invoked(void) 
	return !!rcu_state.n_online_cpus;

}



/*

 * Near the end of the offline process.  Trace the fact that this CPU

 * is going offline.

 */

int rcutree_dying_cpu(unsigned int cpu)

{

	bool blkd;

	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);

	struct rcu_node *rnp = rdp->mynode;



	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))

		return 0;



	blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);

	trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),

			       blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));

	return 0;

}



/*

 * All CPUs for the specified rcu_node structure have gone offline,

 * and all tasks that were preempted within an RCU read-side critical
@@ -4301,23 +4282,6 @@ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) 
	}

}



/*

 * The CPU has been completely removed, and some other CPU is reporting

 * this fact from process context.  Do the remainder of the cleanup.

 * There can only be one CPU hotplug operation at a time, so no need for

 * explicit locking.

 */

int rcutree_dead_cpu(unsigned int cpu)

{

	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))

		return 0;



	WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);

	// Stop-machine done, so allow nohz_full to disable tick.

	tick_dep_clear(TICK_DEP_BIT_RCU);

	return 0;

}



/*

 * Propagate ->qsinitmask bits up the rcu_node tree to account for the

 * first CPU in a given leaf rcu_node structure coming online.  The caller
@@ -4470,29 +4434,6 @@ int rcutree_online_cpu(unsigned int cpu) 
	return 0;

}



/*

 * Near the beginning of the process.  The CPU is still very much alive

 * with pretty much all services enabled.

 */

int rcutree_offline_cpu(unsigned int cpu)

{

	unsigned long flags;

	struct rcu_data *rdp;

	struct rcu_node *rnp;



	rdp = per_cpu_ptr(&rcu_data, cpu);

	rnp = rdp->mynode;

	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	rnp->ffmask &= ~rdp->grpmask;

	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);



	rcutree_affinity_setting(cpu, cpu);



	// nohz_full CPUs need the tick for stop-machine to work quickly

	tick_dep_set(TICK_DEP_BIT_RCU);

	return 0;

}



/*

 * Mark the specified CPU as being online so that subsequent grace periods

 * (both expedited and normal) will wait on it.  Note that this means that
@@ -4646,7 +4587,60 @@ void rcutree_migrate_callbacks(int cpu) 
		  cpu, rcu_segcblist_n_cbs(&rdp->cblist),

		  rcu_segcblist_first_cb(&rdp->cblist));

}

#endif



/*

 * The CPU has been completely removed, and some other CPU is reporting

 * this fact from process context.  Do the remainder of the cleanup.

 * There can only be one CPU hotplug operation at a time, so no need for

 * explicit locking.

 */

int rcutree_dead_cpu(unsigned int cpu)

{

	WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);

	// Stop-machine done, so allow nohz_full to disable tick.

	tick_dep_clear(TICK_DEP_BIT_RCU);

	return 0;

}



/*

 * Near the end of the offline process.  Trace the fact that this CPU

 * is going offline.

 */

int rcutree_dying_cpu(unsigned int cpu)

{

	bool blkd;

	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);

	struct rcu_node *rnp = rdp->mynode;



	blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);

	trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),

			       blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));

	return 0;

}



/*

 * Near the beginning of the process.  The CPU is still very much alive

 * with pretty much all services enabled.

 */

int rcutree_offline_cpu(unsigned int cpu)

{

	unsigned long flags;

	struct rcu_data *rdp;

	struct rcu_node *rnp;



	rdp = per_cpu_ptr(&rcu_data, cpu);

	rnp = rdp->mynode;

	raw_spin_lock_irqsave_rcu_node(rnp, flags);

	rnp->ffmask &= ~rdp->grpmask;

	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);



	rcutree_affinity_setting(cpu, cpu);



	// nohz_full CPUs need the tick for stop-machine to work quickly

	tick_dep_set(TICK_DEP_BIT_RCU);

	return 0;

}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */



/*

 * On non-huge systems, use expedited RCU grace periods to make suspend