On Wed, 14 Aug 2019 17:41:08 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote:
> Commit a9cd410a3d29 ("mm/page_alloc.c: memory hotplug: free pages as higher
> order") assumed that any PFN we get via memory resources is aligned to
> to MAX_ORDER - 1, I am not convinced that is always true. Let's play safe,
> check the alignment and fallback to single pages.
>
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -646,6 +646,9 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
> */
> for (pfn = start_pfn; pfn < end_pfn; pfn += 1ul << order) {
> order = min(MAX_ORDER - 1, get_order(PFN_PHYS(end_pfn - pfn)));
> + /* __free_pages_core() wants pfns to be aligned to the order */
> + if (unlikely(!IS_ALIGNED(pfn, 1ul << order)))
> + order = 0;
> (*online_page_callback)(pfn_to_page(pfn), order);
> }
We aren't sure if this occurs, but if it does, we silently handle it.
It seems a reasonable defensive thing to do, but should we add a
WARN_ON_ONCE() so that we get to find out about it? If we get such a
report then we can remove the WARN_ON_ONCE() and add an illuminating
comment.
