On Wed, Dec 14, 2016 at 09:11:46AM +0000, Ard Biesheuvel wrote:
> The VM_BUG_ON() check in move_freepages() checks whether the node
> id of a page matches the node id of its zone. However, it does this
> before having checked whether the struct page pointer refers to a
> valid struct page to begin with. This is guaranteed in most cases,
> but may not be the case if CONFIG_HOLES_IN_ZONE=y.
>
> So reorder the VM_BUG_ON() with the pfn_valid_within() check.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f64e7bcb43b7..4e298e31fa86 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1864,14 +1864,14 @@ int move_freepages(struct zone *zone,
> #endif
>
> for (page = start_page; page <= end_page;) {
> - /* Make sure we are not inadvertently changing nodes */
> - VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
> -
> if (!pfn_valid_within(page_to_pfn(page))) {
> page++;
> continue;
> }
>
> + /* Make sure we are not inadvertently changing nodes */
> + VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
> +
> if (!PageBuddy(page)) {
> page++;
> continue;
Acked-by: Will Deacon <will.deacon@xxxxxxx>
I'm guessing akpm can pick this up as a non-urgent fix.
Will
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