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Commit d2ba7e2a authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Acked-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1e35eaa2

kernel/cpu.c

+10 −20
Original line number Original line Diff line number Diff line
@@ -33,17 +33,13 @@ static struct { 
	 * an ongoing cpu hotplug operation.

	 * an ongoing cpu hotplug operation.

	 */

	 */

	int refcount;

	int refcount;

	wait_queue_head_t writer_queue;

} cpu_hotplug;

} cpu_hotplug;





#define writer_exists() (cpu_hotplug.active_writer != NULL)



void __init cpu_hotplug_init(void)

void __init cpu_hotplug_init(void)

{

{

	cpu_hotplug.active_writer = NULL;

	cpu_hotplug.active_writer = NULL;

	mutex_init(&cpu_hotplug.lock);

	mutex_init(&cpu_hotplug.lock);

	cpu_hotplug.refcount = 0;

	cpu_hotplug.refcount = 0;

	init_waitqueue_head(&cpu_hotplug.writer_queue);

}

}





#ifdef CONFIG_HOTPLUG_CPU

#ifdef CONFIG_HOTPLUG_CPU
@@ -65,11 +61,8 @@ void put_online_cpus(void) 
	if (cpu_hotplug.active_writer == current)

	if (cpu_hotplug.active_writer == current)

		return;

		return;

	mutex_lock(&cpu_hotplug.lock);

	mutex_lock(&cpu_hotplug.lock);

	cpu_hotplug.refcount--;

	if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))



		wake_up_process(cpu_hotplug.active_writer);

	if (unlikely(writer_exists()) && !cpu_hotplug.refcount)

		wake_up(&cpu_hotplug.writer_queue);



	mutex_unlock(&cpu_hotplug.lock);

	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,

 * Note that during a cpu-hotplug operation, the new readers, if any,

 * will be blocked by the cpu_hotplug.lock

 * will be blocked by the cpu_hotplug.lock

 *

 *

 * Since cpu_maps_update_begin is always called after invoking

 * Since cpu_hotplug_begin() is always called after invoking

 * cpu_maps_update_begin, we can be sure that only one writer is active.

 * cpu_maps_update_begin(), we can be sure that only one writer is active.

 *

 *

 * Note that theoretically, there is a possibility of a livelock:

 * Note that theoretically, there is a possibility of a livelock:

 * - Refcount goes to zero, last reader wakes up the sleeping

 * - 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)

static void cpu_hotplug_begin(void)

{

{

	DECLARE_WAITQUEUE(wait, current);

	cpu_hotplug.active_writer = current;





	for (;;) {

		mutex_lock(&cpu_hotplug.lock);

		mutex_lock(&cpu_hotplug.lock);



		if (likely(!cpu_hotplug.refcount))

	cpu_hotplug.active_writer = current;

			break;

	add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);

		__set_current_state(TASK_UNINTERRUPTIBLE);

	while (cpu_hotplug.refcount) {

		set_current_state(TASK_UNINTERRUPTIBLE);

		mutex_unlock(&cpu_hotplug.lock);

		mutex_unlock(&cpu_hotplug.lock);

		schedule();

		schedule();

		mutex_lock(&cpu_hotplug.lock);

	}

	}

	remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);

}

}





static void cpu_hotplug_done(void)

static void cpu_hotplug_done(void)