linux-kernel - [PATCH 1/2] cpuhotplug: do not need cpu_hotplug_begin() when CONFIG_HOTPLUG

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Message-ID: <4BB9BD86.4030802@cn.fujitsu.com>
Date:	Mon, 05 Apr 2010 18:37:58 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Gautham R Shenoy <ego@...ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nathan Fontenot <nfont@...tin.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Sachin Sant <sachinp@...ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Shane Wang <shane.wang@...el.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] cpuhotplug: do not need cpu_hotplug_begin() when CONFIG_HOTPLUG_CPU=n


Since when CONFIG_HOTPLUG_CPU=n, get_online_cpus() do nothing,
so we don't need cpu_hotplug_begin() either.

This patch moves cpu_hotplug_begin()/cpu_hotplug_done()
into the code block of CONFIG_HOTPLUG_CPU=y.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 8d340fa..bc1e3d5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -19,6 +19,20 @@
 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
 static DEFINE_MUTEX(cpu_add_remove_lock);
 
+/*
+ * The following two API's must be used when attempting
+ * to serialize the updates to cpu_online_mask, cpu_present_mask.
+ */
+void cpu_maps_update_begin(void)
+{
+	mutex_lock(&cpu_add_remove_lock);
+}
+
+void cpu_maps_update_done(void)
+{
+	mutex_unlock(&cpu_add_remove_lock);
+}
+
 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
 
 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
@@ -26,6 +40,8 @@ static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  */
 static int cpu_hotplug_disabled;
 
+#ifdef CONFIG_HOTPLUG_CPU
+
 static struct {
 	struct task_struct *active_writer;
 	struct mutex lock; /* Synchronizes accesses to refcount, */
@@ -40,8 +56,6 @@ static struct {
 	.refcount = 0,
 };
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 void get_online_cpus(void)
 {
 	might_sleep();
@@ -66,22 +80,6 @@ void put_online_cpus(void)
 }
 EXPORT_SYMBOL_GPL(put_online_cpus);
 
-#endif	/* CONFIG_HOTPLUG_CPU */
-
-/*
- * The following two API's must be used when attempting
- * to serialize the updates to cpu_online_mask, cpu_present_mask.
- */
-void cpu_maps_update_begin(void)
-{
-	mutex_lock(&cpu_add_remove_lock);
-}
-
-void cpu_maps_update_done(void)
-{
-	mutex_unlock(&cpu_add_remove_lock);
-}
-
 /*
  * This ensures that the hotplug operation can begin only when the
  * refcount goes to zero.
@@ -123,6 +121,12 @@ static void cpu_hotplug_done(void)
 	cpu_hotplug.active_writer = NULL;
 	mutex_unlock(&cpu_hotplug.lock);
 }
+
+#else /* #if CONFIG_HOTPLUG_CPU */
+static void cpu_hotplug_begin(void) {}
+static void cpu_hotplug_done(void) {}
+#endif	/* #esle #if CONFIG_HOTPLUG_CPU */
+
 /* Need to know about CPUs going up/down? */
 int __ref register_cpu_notifier(struct notifier_block *nb)
 {

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