linux-kernel - Re: [PATCH 4/4] memory_hotplug: use pgdat_resize_lock() when updating node_present

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Date:	Wed, 1 May 2013 15:30:52 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] memory_hotplug: use pgdat_resize_lock() when updating
 node_present_pages

On Wed, 1 May 2013, Cody P Schafer wrote:

> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index a221fac..0bdca10 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -915,6 +915,7 @@ static void node_states_set_node(int node, struct memory_notify *arg)
>  
>  int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
>  {
> +	unsigned long flags;
>  	unsigned long onlined_pages = 0;
>  	struct zone *zone;
>  	int need_zonelists_rebuild = 0;
> @@ -993,7 +994,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  
>  	zone->managed_pages += onlined_pages;
>  	zone->present_pages += onlined_pages;
> +
> +	pgdat_resize_lock(zone->zone_pgdat, &flags);
>  	zone->zone_pgdat->node_present_pages += onlined_pages;
> +	pgdat_resize_unlock(zone->zone_pgdat, &flags);
> +
>  	if (onlined_pages) {
>  		node_states_set_node(zone_to_nid(zone), &arg);
>  		if (need_zonelists_rebuild)

Why?  You can't get a partial read of a word-sized data structure.
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