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Subject[PATCH 1/2] CPU hotplug: Export cpu_hotplug_begin() interface
Date
cpu_hotplug_begin() and cpu_hotplug_done() are the interfaces to
acquire the writer lock of the cpu_hotplug.lock. The interfaces are
used along with cpu_maps_update_begin() / cpu_maps_update_done() to
serialize the updates to the system cpu maps, such as cpu_online_mask
and cpu_present_mask.

cpu_present_mask is updated by the ACPI processor handler. Therefore,
this patch changes the interfaces to global, and exports them in cpu.h.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
include/linux/cpu.h | 4 ++++
kernel/cpu.c | 9 +++------
2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index ab0eade..956c0a1 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -172,6 +172,8 @@ extern struct bus_type cpu_subsys;
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */

+extern void cpu_hotplug_begin(void);
+extern void cpu_hotplug_done(void);
extern void get_online_cpus(void);
extern void put_online_cpus(void);
extern void cpu_hotplug_disable(void);
@@ -197,6 +199,8 @@ static inline void cpu_hotplug_driver_unlock(void)

#else /* CONFIG_HOTPLUG_CPU */

+static inline void cpu_hotplug_begin(void) {}
+static inline void cpu_hotplug_done(void) {}
#define get_online_cpus() do { } while (0)
#define put_online_cpus() do { } while (0)
#define cpu_hotplug_disable() do { } while (0)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index b2b227b..d7f07a2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -113,7 +113,7 @@ EXPORT_SYMBOL_GPL(put_online_cpus);
* get_online_cpus() not an api which is called all that often.
*
*/
-static void cpu_hotplug_begin(void)
+void cpu_hotplug_begin(void)
{
cpu_hotplug.active_writer = current;

@@ -127,7 +127,7 @@ static void cpu_hotplug_begin(void)
}
}

-static void cpu_hotplug_done(void)
+void cpu_hotplug_done(void)
{
cpu_hotplug.active_writer = NULL;
mutex_unlock(&cpu_hotplug.lock);
@@ -154,10 +154,7 @@ void cpu_hotplug_enable(void)
cpu_maps_update_done();
}

-#else /* #if CONFIG_HOTPLUG_CPU */
-static void cpu_hotplug_begin(void) {}
-static void cpu_hotplug_done(void) {}
-#endif /* #else #if CONFIG_HOTPLUG_CPU */
+#endif /* CONFIG_HOTPLUG_CPU */

/* Need to know about CPUs going up/down? */
int __ref register_cpu_notifier(struct notifier_block *nb)

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