Commit ef126206 authored Feb 28, 2018 by Paul E. McKenney

rcu: Don't allocate rcu_nocb_mask if no one needs it

Commit 44c65ff2 ("rcu: Eliminate NOCBs CPU-state Kconfig options")
made allocation of rcu_nocb_mask depend only on the rcu_nocbs=,
nohz_full=, or isolcpus= kernel boot parameters. However, it failed
to change the initial value of rcu_init_nohz()'s local variable
need_rcu_nocb_mask to false, which can result in useless allocation
of an all-zero rcu_nocb_mask. This commit therefore fixes this bug by
changing the initial value of need_rcu_nocb_mask to false.

While we are in the area, also correct the error message that is printed
when someone specifies that can-never-exist CPUs should be NOCBs CPUs.

Reported-by: Byungchul Park <byungchul.park@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Byungchul Park <byungchul.park@lge.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>

parent be01b4ca

kernel/rcu/tree_plugin.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -2283,7 +2283,7 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
		void __init rcu_init_nohz(void)
		{
		int cpu;
		bool need_rcu_nocb_mask = true;
		bool need_rcu_nocb_mask = false;
		struct rcu_state *rsp;

		#if defined(CONFIG_NO_HZ_FULL)
		@@ -2306,7 +2306,7 @@ void __init rcu_init_nohz(void)
		#endif /* #if defined(CONFIG_NO_HZ_FULL) */

		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
		pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
		pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
		cpumask_and(rcu_nocb_mask, cpu_possible_mask,
		rcu_nocb_mask);
		}

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