On 12/16/2014 12:03 AM, akpm@xxxxxxxxxxxxxxxxxxxx wrote:
> From: James Custer <jcuster@xxxxxxx>
> Subject: mm: fix invalid use of pfn_valid_within in test_pages_in_a_zone
>
> Offlining memory by 'echo 0 > /sys/devices/system/memory/memory#/online'
> or reading valid_zones 'cat
> /sys/devices/system/memory/memory#/valid_zones' causes BUG: unable to
> handle kernel paging request due to invalid use of pfn_valid_within. This
> is due to a bug in test_pages_in_a_zone.
It would still be useful to show the BUG, and provide /proc/zoneinfo for us to
see where are the corner cases.
> In order to use pfn_valid_within within a MAX_ORDER_NR_PAGES block of
> pages, a valid pfn within the block must first be found. There only needs
> to be one valid pfn found in test_pages_in_a_zone in the first place. So
> the fix is to replace pfn_valid_within with pfn_valid such that the first
> valid pfn within the pageblock is found (if it exists). This works
> independently of CONFIG_HOLES_IN_ZONE.
>
> Signed-off-by: James Custer <jcuster@xxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Cc: Russ Anderson <rja@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> mm/memory_hotplug.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff -puN mm/memory_hotplug.c~mm-fix-invalid-use-of-pfn_valid_within-in-test_pages_in_a_zone mm/memory_hotplug.c
> --- a/mm/memory_hotplug.c~mm-fix-invalid-use-of-pfn_valid_within-in-test_pages_in_a_zone
> +++ a/mm/memory_hotplug.c
> @@ -1331,7 +1331,7 @@ int is_mem_section_removable(unsigned lo
> }
>
> /*
> - * Confirm all pages in a range [start, end) is belongs to the same zone.
> + * Confirm all pages in a range [start, end) belong to the same zone.
> */
> int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
> {
> @@ -1342,10 +1342,11 @@ int test_pages_in_a_zone(unsigned long s
> for (pfn = start_pfn;
> pfn < end_pfn;
> pfn += MAX_ORDER_NR_PAGES) {
> - i = 0;
> - /* This is just a CONFIG_HOLES_IN_ZONE check.*/
> - while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i))
> - i++;
> + /* Find the first valid pfn in this pageblock */
> + for (i = 0; i < MAX_ORDER_NR_PAGES; i++) {
> + if (pfn_valid(pfn + i))
> + break;
> + }
> if (i == MAX_ORDER_NR_PAGES)
> continue;
> page = pfn_to_page(pfn + i);
> _
>
> --
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