Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback registration functions

[Oleg Nesterov]

On 02/12, Srivatsa S. Bhat wrote:
>
> On 02/11/2014 10:45 PM, Oleg Nesterov wrote:
> >
> > I am a bit confused... If we do this, why we can't simply turn
> > cpu_add_remove_lock into rw_semaphore?

[...snip...]

> 	cpu_notifier_register_begin();                |  Run in parallel
>                                                       |  with similar phases
> 	for_each_online_cpu(cpu)                      |  from other subsystems.
> 		init_cpu(cpu);                        |
>
> 	/* Updates the cpu notifier chain. */
> 	register_cpu_notifier(&foobar_cpu_notifier); ||| -- Must run serially

Ah indeed, we can't use a single lock, thanks. Perhaps we can simply
add a spinlock_t which only protects cpu_chain though, but I am not
sure and currently this is off-topic anyway.

Thanks,

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/