Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside of zone_span_writelock()

[Ni zhan Chen <nizhan.chen@gmail.com>]

On 09/27/2012 02:47 PM, Lai Jiangshan wrote:
> The __add_zone() maybe call sleep-able init_currently_empty_zone()
> to init wait_table,
>
> But this function also modifies the zone_start_pfn without any lock.
> It is bugy.
>
> 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@csn.ul.ie>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@jp.fujitsu.com>
> Tested-by: Wen Congyang <wency@cn.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;
>   
>   	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;
> -

then how can mminit_dprintk print zone->zone_start_pfn ? always print 0 
make no sense.

>   	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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