Commit-ID: ef12620626e4e6a062acd9701d1d3429b2356773
Gitweb: https://git.kernel.org/tip/ef12620626e4e6a062acd9701d1d3429b2356773
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 28 Feb 2018 10:34:54 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 15 May 2018 10:27:11 -0700
rcu: Don't allocate rcu_nocb_mask if no one needs it
Commit 44c65ff2e3b0 ("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@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: Byungchul Park <byungchul.park@xxxxxxx>
Tested-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 6c5df18bbf2f..3566e4f6dfcc 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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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