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authorOleg Nesterov <oleg@tv-sign.ru>2008-04-29 01:00:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-29 08:06:11 -0700
commitd2ba7e2ae206e9ab24e8937d99d0d5513bfd08e5 (patch)
tree4cdd43bbf03885705fed5c80e982d19d397afaeb /kernel/cpu.c
parent1e35eaa2d86419470f3f3aed9acd85b8addff25c (diff)
simplify cpu_hotplug_begin()/put_online_cpus()
cpu_hotplug_begin() must be always called under cpu_add_remove_lock, this means that only one process can be cpu_hotplug.active_writer. So we don't need the cpu_hotplug.writer_queue, we can wake up the ->active_writer directly. Also, fix the comment. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Dipankar Sarma <dipankar@in.ibm.com> Acked-by: Gautham R Shenoy <ego@in.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c30
1 files changed, 10 insertions, 20 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index f8f9468d17d7..a98f6ab16ecd 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -33,17 +33,13 @@ static struct {
* an ongoing cpu hotplug operation.
*/
int refcount;
- wait_queue_head_t writer_queue;
} cpu_hotplug;
-#define writer_exists() (cpu_hotplug.active_writer != NULL)
-
void __init cpu_hotplug_init(void)
{
cpu_hotplug.active_writer = NULL;
mutex_init(&cpu_hotplug.lock);
cpu_hotplug.refcount = 0;
- init_waitqueue_head(&cpu_hotplug.writer_queue);
}
#ifdef CONFIG_HOTPLUG_CPU
@@ -65,11 +61,8 @@ void put_online_cpus(void)
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
- cpu_hotplug.refcount--;
-
- if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
- wake_up(&cpu_hotplug.writer_queue);
-
+ if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
+ wake_up_process(cpu_hotplug.active_writer);
mutex_unlock(&cpu_hotplug.lock);
}
@@ -98,8 +91,8 @@ void cpu_maps_update_done(void)
* Note that during a cpu-hotplug operation, the new readers, if any,
* will be blocked by the cpu_hotplug.lock
*
- * Since cpu_maps_update_begin is always called after invoking
- * cpu_maps_update_begin, we can be sure that only one writer is active.
+ * Since cpu_hotplug_begin() is always called after invoking
+ * cpu_maps_update_begin(), we can be sure that only one writer is active.
*
* Note that theoretically, there is a possibility of a livelock:
* - Refcount goes to zero, last reader wakes up the sleeping
@@ -115,19 +108,16 @@ void cpu_maps_update_done(void)
*/
static void cpu_hotplug_begin(void)
{
- DECLARE_WAITQUEUE(wait, current);
-
- mutex_lock(&cpu_hotplug.lock);
-
cpu_hotplug.active_writer = current;
- add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);
- while (cpu_hotplug.refcount) {
- set_current_state(TASK_UNINTERRUPTIBLE);
+
+ for (;;) {
+ mutex_lock(&cpu_hotplug.lock);
+ if (likely(!cpu_hotplug.refcount))
+ break;
+ __set_current_state(TASK_UNINTERRUPTIBLE);
mutex_unlock(&cpu_hotplug.lock);
schedule();
- mutex_lock(&cpu_hotplug.lock);
}
- remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
}
static void cpu_hotplug_done(void)

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