On 11/15, Gautham R Shenoy wrote:
>
> +static struct {
> + struct task_struct *active_writer;
> + struct mutex lock; /* Synchronizes accesses to refcount, */
> + /*
> + * Also blocks the new readers during
> + * an ongoing cpu hotplug operation.
> + */
> + int refcount;
> + wait_queue_head_t writer_queue;
> +} cpu_hotplug;
> ...
> void unlock_cpu_hotplug(void)
> {
> - WARN_ON(recursive != current);
> - if (recursive_depth) {
> - recursive_depth--;
> + if (cpu_hotplug.active_writer == current)
> return;
> - }
> - recursive = NULL;
> - mutex_unlock(&cpu_bitmask_lock);
> + mutex_lock(&cpu_hotplug.lock);
> + cpu_hotplug.refcount--;
> +
> + if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
> + wake_up(&cpu_hotplug.writer_queue);
> +
> + mutex_unlock(&cpu_hotplug.lock);
> +
> }
> ...
> +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);
> + mutex_unlock(&cpu_hotplug.lock);
> + schedule();
> + mutex_lock(&cpu_hotplug.lock);
> + }
> + remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
> +}
Perhaps we can simplify this a little bit? I don't think we really need
cpu_hotplug.writer_queue, afaics we can just do
void unlock_cpu_hotplug(void)
{
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
if (!--cpu_hotplug.refcount && cpu_hotplug.active_writer)
wake_up_process(cpu_hotplug.active_writer);
mutex_unlock(&cpu_hotplug.lock);
}
static void cpu_hotplug_begin(void)
{
mutex_lock(&cpu_hotplug.lock);
cpu_hotplug.active_writer = current;
while (cpu_hotplug.refcount) {
__set_current_state(TASK_UNINTERRUPTIBLE);
mutex_unlock(&cpu_hotplug.lock);
schedule();
mutex_lock(&cpu_hotplug.lock);
}
}
(not that it matters, we can do this later even if I am right)
Oleg.
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