On Sat, Mar 10, 2018 at 12:51 AM, <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> From: Daniel Vacek <neelx@xxxxxxxxxx>
> Subject: mm/page_alloc: fix memmap_init_zone pageblock alignment
>
> b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns where
> possible") introduced a bug where move_freepages() triggers a VM_BUG_ON()
> on uninitialized page structure due to pageblock alignment. To fix this,
> simply align the skipped pfns in memmap_init_zone() the same way as in
> move_freepages_block().
>
> diff -puN mm/page_alloc.c~mm-page_alloc-fix-memmap_init_zone-pageblock-alignment mm/page_alloc.c
> --- a/mm/page_alloc.c~mm-page_alloc-fix-memmap_init_zone-pageblock-alignment
> +++ a/mm/page_alloc.c
> @@ -5359,9 +5359,14 @@ void __meminit memmap_init_zone(unsigned
> /*
> * Skip to the pfn preceding the next valid one (or
> * end_pfn), such that we hit a valid pfn (or end_pfn)
> - * on our next iteration of the loop.
> + * on our next iteration of the loop. Note that it needs
> + * to be pageblock aligned even when the region itself
> + * is not. move_freepages_block() can shift ahead of
> + * the valid region but still depends on correct page
> + * metadata.
> */
> - pfn = memblock_next_valid_pfn(pfn, end_pfn) - 1;
> + pfn = (memblock_next_valid_pfn(pfn, end_pfn) &
> + ~(pageblock_nr_pages-1)) - 1;
Again, end_pfn should be gone.
--nX
> #endif
> continue;
> }
> _