Re: [PATCH 2/2] mm: drop hotplug lock from lru_add_drain_all

[Michal Hocko]

On Thu 02-11-17 10:36:13, Michal Hocko wrote:
[...]
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 67330a438525..8c6e9c6d194c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6830,8 +6830,12 @@ void __init free_area_init(unsigned long *zones_size)
>  
>  static int page_alloc_cpu_dead(unsigned int cpu)
>  {
> +     unsigned long flags;
>  
> +     local_irq_save(flags);
>       lru_add_drain_cpu(cpu);
> +     local_irq_restore(flags);
> +
>       drain_pages(cpu);
  
I was staring into the hotplug code and tried to understand the context
this callback runs in and AFAIU IRQ disabling is not needed at all
because cpuhp_thread_fun runs with IRQ disabled when offlining an online
cpu. I have a bit hard time to follow the code due to all the
indirection so please correct me if I am wrong.
-- 
Michal Hocko
SUSE Labs