linux-kernel - Re: [PATCH 2/2] mm: drop hotplug lock from lru_add_drain

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Message-ID: <20171102123749.zwnlsvpoictnmp53@dhcp22.suse.cz>
Date:   Thu, 2 Nov 2017 13:37:49 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     linux-mm@...ck.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: drop hotplug lock from lru_add_drain_all

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