(sorry if this was already discussed, I ignored most of my emails
I got this week)
On 12/09, David Hildenbrand wrote:
>
> @@ -116,7 +118,13 @@ void put_online_cpus(void)
> if (cpu_hotplug.active_writer == current)
> return;
> if (!mutex_trylock(&cpu_hotplug.lock)) {
> + /* inc before testing for active_writer to not lose wake ups */
> atomic_inc(&cpu_hotplug.puts_pending);
> + spin_lock(&cpu_hotplug.awr_lock);
> + /* we might be the last one */
> + if (unlikely(cpu_hotplug.active_writer))
> + wake_up_process(cpu_hotplug.active_writer);
> + spin_unlock(&cpu_hotplug.awr_lock);
Not sure I understand. awr_lock can only ensure that active_writer
can't go away.
Why active_writer should see .puts_pending != 0 if this is called
right after cpu_hotplug_begin() takes cpu_hotplug.lock but before
it sets TASK_UNINTERRUPTIBLE?
IOW,
> void cpu_hotplug_begin(void)
> {
> + spin_lock(&cpu_hotplug.awr_lock);
> cpu_hotplug.active_writer = current;
> + spin_unlock(&cpu_hotplug.awr_lock);
>
> cpuhp_lock_acquire();
> for (;;) {
> mutex_lock(&cpu_hotplug.lock);
> + __set_current_state(TASK_UNINTERRUPTIBLE);
don't we need set_current_state() here ?
Oleg.
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