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Commit ef126206 authored by Paul E. McKenney's avatar Paul E. McKenney
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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: default avatarByungchul Park <byungchul.park@lge.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarByungchul Park <byungchul.park@lge.com>
Tested-by: default avatarNicholas 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);

	}