Re: [PATCH] drivers: memory: check for missing sections when testing zones

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 3 Dec 2015 11:58:46 -0600 Andrew Banman <abanman@sgi.com> wrote:

> test_pages_in_a_zone does not account for the possibility of missing sections
> in the given pfn range. Since pfn_valid_within always returns 1 when
> CONFIG_HOLES_IN_ZONE is not set, invalid pfns from missing sections
> will pass the test, resulting in a kernel oops. This is remedied by simply
> checking for the presence of the pfn's section. We don't have to remove
> the pfn_valid_within optimization.
> 
> The patch also prevents a crash from offlining memory devices with missing
> sections. Despite this, it's probably best to keep
> 
> [PATCH 3/3] drivers: memory: prohibit offlining of memory blocks withmissing sections
> 
> because missing sections may indicate other problems, like overlapping mem
> blocks and who knows what else (see the discussion at BZ 107781).
> 
> ---
>  mm/memory_hotplug.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 67d488a..74f5bcd 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1383,6 +1383,9 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
>              pfn < end_pfn;
>              pfn += MAX_ORDER_NR_PAGES) {
>                 i = 0;
> +               /* Make sure the memory section is present */
> +               if (!present_section_nr(pfn_to_section_nr(pfn)))
> +                       continue;
>                 /* This is just a CONFIG_HOLES_IN_ZONE check.*/
>                 while ((i < MAX_ORDER_NR_PAGES) && !pfn_valid_within(pfn + i))
>                         i++;

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Please confirm that this patch is applicable to current mainline.

Please confirm that this patch is suitable for backporting into -stable
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Thanks.