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simplify cpu_hotplug_begin()/put_online_cpus()

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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>
This commit is contained in:
Oleg Nesterov 2008-04-29 01:00:29 -07:00 committed by Linus Torvalds
parent 1e35eaa2d8
commit d2ba7e2ae2
1 changed files with 10 additions and 20 deletions
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30
kernel/cpu.c
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@ -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)