Re: [PATCH v2 5/5] mm/page_alloc.c: avoid allocating highmem pages via alloc_pages_exact[_nid]

David Hildenbrand
2021-09-02T12:16:23Z

On 02.09.21 14:12, Miaohe Lin wrote:
> Don't use with __GFP_HIGHMEM because page_address() cannot represent
> highmem pages without kmap(). Newly allocated pages would leak as
> page_address() will return NULL for highmem pages here. But It works
> now because the callers do not specify __GFP_HIGHMEM now.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> mm/page_alloc.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9c09dcb24149..e1d0e27d005a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5614,8 +5614,8 @@ void *alloc_pages_exact(size_t size, gfp_t gfp_mask)
> unsigned int order = get_order(size);
> unsigned long addr;
>
> - if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
> - gfp_mask &= ~__GFP_COMP;
> + if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
> + gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
>
> addr = __get_free_pages(gfp_mask, order);
> return make_alloc_exact(addr, order, size);
> @@ -5639,8 +5639,8 @@ void * __meminit alloc_pages_exact_nid(int nid, size_t size, gfp_t gfp_mask)
> unsigned int order = get_order(size);
> struct page *p;
>
> - if (WARN_ON_ONCE(gfp_mask & __GFP_COMP))
> - gfp_mask &= ~__GFP_COMP;
> + if (WARN_ON_ONCE(gfp_mask & (__GFP_COMP | __GFP_HIGHMEM)))
> + gfp_mask &= ~(__GFP_COMP | __GFP_HIGHMEM);
>
> p = alloc_pages_node(nid, gfp_mask, order);
> if (!p)
>

Ideally we would convert this WARN_ON_ONCE() to pr_warn_once(), but I
guess this really never ever happens on a production system and would
get caught early while testing.

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb