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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 03/22] rcu: Don't allocate rcu_nocb_mask if no one needs it
Date: Sun, 22 Apr 2018 19:32:08 -0700	[thread overview]
Message-ID: <1524450747-22778-3-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180423023150.GA21533@linux.vnet.ibm.com>

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@lge.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Byungchul Park <byungchul.park@lge.com>
---
 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);
 	}
-- 
2.5.2

  parent reply	other threads:[~2018-04-23  2:35 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-23  2:31 [PATCH tip/core/rcu 0/22] Miscellaneous fixes for v4.18 Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU Paul E. McKenney
2018-04-23  8:51   ` Peter Zijlstra
2018-04-23 12:40     ` Paul E. McKenney
2018-04-23 13:47       ` Steven Rostedt
2018-04-23 14:10         ` Peter Zijlstra
2018-04-23 14:35           ` Steven Rostedt
2018-04-23 15:47             ` Paul E. McKenney
2018-04-23 19:12               ` Paul E. McKenney
2018-04-23 14:03       ` Peter Zijlstra
2018-04-23  2:32 ` [PATCH tip/core/rcu 02/22] rcu: Inline rcu_preempt_do_callback() into its sole caller Paul E. McKenney
2018-04-23  2:32 ` Paul E. McKenney [this message]
2018-04-23  2:32 ` [PATCH tip/core/rcu 04/22] rcu: Call wake_nocb_leader_defer() with 'FORCE' when nocb_q_count is high Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 05/22] rcu: Remove deprecated RCU debugfs tracing code Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 06/22] rcu: Rename cond_resched_rcu_qs() to cond_resched_tasks_rcu_qs() Paul E. McKenney
2018-04-23  8:53   ` Peter Zijlstra
2018-04-23 12:32     ` Paul E. McKenney
2018-04-23 12:48       ` Peter Zijlstra
2018-04-23 13:12         ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 07/22] softirq: Eliminate unused cond_resched_softirq() macro Paul E. McKenney
2018-04-23  8:54   ` Peter Zijlstra
2018-04-23 13:25     ` Eric Dumazet
2018-04-23 19:10       ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 08/22] rcu: Move __rcu_read_lock() and __rcu_read_unlock() to tree_plugin.h Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 09/22] rcu: Update rcu_bind_gp_kthread() header comment Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 10/22] rcu: Declare rcu_eqs_special_set() in public header Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 11/22] srcu: Add cleanup_srcu_struct_quiesced() Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 12/22] nvme: Avoid flush dependency in delete controller flow Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 13/22] rcu: Exclude near-simultaneous RCU CPU stall warnings Paul E. McKenney
2018-05-03 18:22   ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 14/22] rcu: Add leaf-node macros Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 15/22] doc: Ensure whatisRCU.txt actually says what RCU is Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 16/22] EXP: rcu: Add debugging info to assertion Paul E. McKenney
2018-05-03 18:23   ` Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 17/22] EXP: rcu: Abstract addition of debugging information " Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 18/22] EXP: rcu: Add ->boost_tasks " Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 19/22] EXP: rcu: Add debugging info to other assertion Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 20/22] EXP rcu: Add ->qsmask to assertion Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 21/22] EXP rcu: Add checks for setting ->gp_flags Paul E. McKenney
2018-04-23  2:32 ` [PATCH tip/core/rcu 22/22] rcu: Use the proper lockdep annotation in dump_blkd_tasks() Paul E. McKenney

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