On Sat, Feb 16, 2008 at 08:22:54PM +0300, Oleg Nesterov wrote:
This looks neat and clean.
Acked-by: Gautham R Shenoy <[EMAIL PROTECTED]>
> 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 <[EMAIL PROTECTED]>
>
> --- 25/kernel/cpu.c~1_CPU_HP_LOCK 2008-02-15 16:59:17.000000000 +0300
> +++ 25/kernel/cpu.c 2008-02-16 18:36:37.000000000 +0300
> @@ -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)
--
Thanks and Regards
gautham
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