Commit f1ffec1e authored by Zhen Lei's avatar Zhen Lei Committed by Paul E. McKenney
Browse files

rcu: Simplify rcu_init_nohz() cpumask handling 



In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or
CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask.
Except that kernels booted without the rcu_nocbs= will not have
allocated rcu_nocb_mask.  And the current rcu_init_nohz() function uses
its need_rcu_nocb_mask and offload_all local variables to track the
rcu_nocb and nohz_full state.

But there is a much simpler approach, namely creating a cpumask pointer
to track the default and then using cpumask_available() to check the
rcu_nocb_mask state.  This commit takes this approach, thereby simplifying
and shortening the rcu_init_nohz() function.

Signed-off-by: default avatarZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 9abf2313

kernel/rcu/tree_nocb.h

+11 −23
Original line number Diff line number Diff line
@@ -1210,45 +1210,33 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload); 
void __init rcu_init_nohz(void)

{

	int cpu;

	bool need_rcu_nocb_mask = false;

	bool offload_all = false;

	struct rcu_data *rdp;



#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)

	if (!rcu_state.nocb_is_setup) {

		need_rcu_nocb_mask = true;

		offload_all = true;

	}

#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */

	const struct cpumask *cpumask = NULL;



#if defined(CONFIG_NO_HZ_FULL)

	if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) {

		need_rcu_nocb_mask = true;

		offload_all = false; /* NO_HZ_FULL has its own mask. */

	}

#endif /* #if defined(CONFIG_NO_HZ_FULL) */

	if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))

		cpumask = tick_nohz_full_mask;

#endif



	if (need_rcu_nocb_mask) {

	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&

	    !rcu_state.nocb_is_setup && !cpumask)

		cpumask = cpu_possible_mask;



	if (cpumask) {

		if (!cpumask_available(rcu_nocb_mask)) {

			if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {

				pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");

				return;

			}

		}



		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);

		rcu_state.nocb_is_setup = true;

	}



	if (!rcu_state.nocb_is_setup)

		return;



#if defined(CONFIG_NO_HZ_FULL)

	if (tick_nohz_full_running)

		cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);

#endif /* #if defined(CONFIG_NO_HZ_FULL) */



	if (offload_all)

		cpumask_setall(rcu_nocb_mask);



	if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {

		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");

		cpumask_and(rcu_nocb_mask, cpu_possible_mask,