linux-kernel - [PATCH v3 2/2] cpu/hotplug: Initialise all cpuhp_cpu

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Date:   Mon, 11 Apr 2022 16:22:33 +0100
From:   Steven Price <steven.price@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Vincent Donnefort <vincent.donnefort@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Price <steven.price@....com>, linux-kernel@...r.kernel.org,
        Baokun Li <libaokun1@...wei.com>,
        Dongli Zhang <dongli.zhang@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Yuan ZhaoXiong <yuanzhaoxiong@...du.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: [PATCH v3 2/2] cpu/hotplug: Initialise all cpuhp_cpu_state structs earlier

Rather than waiting until a CPU is first brought online, do the
initialisation of the cpuhp_cpu_state structure for each CPU during the
__init phase. This saves a (small) amount of non-__init memory and
avoids potential confusion about when the cpuhp_cpu_state struct is
valid.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Steven Price <steven.price@....com>
---
 kernel/cpu.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 5601216eb51b..65903cb10a55 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -715,14 +715,6 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 /*
  * The cpu hotplug threads manage the bringup and teardown of the cpus
  */
-static void cpuhp_create(unsigned int cpu)
-{
-	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
-
-	init_completion(&st->done_up);
-	init_completion(&st->done_down);
-}
-
 static int cpuhp_should_run(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
@@ -882,15 +874,27 @@ static int cpuhp_kick_ap_work(unsigned int cpu)
 
 static struct smp_hotplug_thread cpuhp_threads = {
 	.store			= &cpuhp_state.thread,
-	.create			= &cpuhp_create,
 	.thread_should_run	= cpuhp_should_run,
 	.thread_fn		= cpuhp_thread_fun,
 	.thread_comm		= "cpuhp/%u",
 	.selfparking		= true,
 };
 
+static __init void cpuhp_init_state(void)
+{
+	struct cpuhp_cpu_state *st;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		st = per_cpu_ptr(&cpuhp_state, cpu);
+		init_completion(&st->done_up);
+		init_completion(&st->done_down);
+	}
+}
+
 void __init cpuhp_threads_init(void)
 {
+	cpuhp_init_state();
 	BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
 	kthread_unpark(this_cpu_read(cpuhp_state.thread));
 }
-- 
2.25.1