linux-kernel - Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside of zone_span

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Date:	Thu, 27 Sep 2012 18:30:41 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Xishi Qiu <qiuxishi@...wei.com>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	kosaki.motohiro@...il.com
Subject: Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside
 of zone_span_writelock()

(9/27/12 2:47 AM), Lai Jiangshan wrote:
> The __add_zone() maybe call sleep-able init_currently_empty_zone()
> to init wait_table,

This doesn't explain why sleepable is critical important. I think sleepable
is jsut unrelated. The fact is only: to write zone->zone_start_pfn require
zone_span_writelock, but init_currently_empty_zone() doesn't take it.


> 
> But this function also modifies the zone_start_pfn without any lock.
> It is bugy.

buggy?


> So we move this modification out, and we ensure the modification
> of zone_start_pfn is only done with zone_span_writelock() held or in booting.
> 
> Since zone_start_pfn is not modified by init_currently_empty_zone()
> grow_zone_span() needs to check zone_start_pfn before update it.
> 
> CC: Mel Gorman <mel@....ul.ie>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@...fujitsu.com>
> Tested-by: Wen Congyang <wency@...fujitsu.com>
> ---
>  mm/memory_hotplug.c |    2 +-
>  mm/page_alloc.c     |    3 +--
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b62d429b..790561f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -205,7 +205,7 @@ static void grow_zone_span(struct zone *zone, unsigned long start_pfn,
>  	zone_span_writelock(zone);
>  
>  	old_zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
> -	if (start_pfn < zone->zone_start_pfn)
> +	if (!zone->zone_start_pfn || start_pfn < zone->zone_start_pfn)
>  		zone->zone_start_pfn = start_pfn;

Wrong. zone->zone_start_pfn==0 may be valid pfn. You shouldn't assume it is uninitialized
value.


>  
>  	zone->spanned_pages = max(old_zone_end_pfn, end_pfn) -
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c13ea75..2545013 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3997,8 +3997,6 @@ int __meminit init_currently_empty_zone(struct zone *zone,
>  		return ret;
>  	pgdat->nr_zones = zone_idx(zone) + 1;
>  
> -	zone->zone_start_pfn = zone_start_pfn;
> -
>  	mminit_dprintk(MMINIT_TRACE, "memmap_init",
>  			"Initialising map node %d zone %lu pfns %lu -> %lu\n",
>  			pgdat->node_id,
> @@ -4465,6 +4463,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
>  		ret = init_currently_empty_zone(zone, zone_start_pfn,
>  						size, MEMMAP_EARLY);
>  		BUG_ON(ret);
> +		zone->zone_start_pfn = zone_start_pfn;
>  		memmap_init(size, nid, j, zone_start_pfn);
>  		zone_start_pfn += size;
>  	}
> 

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