On 4/17/21 4:45 AM, Matthew Wilcox (Oracle) wrote:
> If you pass a const pointer to compound_head(), you get a const pointer
> back; if you pass a mutable pointer, you get a mutable pointer back.
> Also remove an unnecessary forward definition of struct page; we're about
> to dereference page->compound_head, so it must already have been defined.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> include/linux/page-flags.h | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index 04a34c08e0a6..d8e26243db25 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -177,17 +177,17 @@ enum pageflags {
>
> #ifndef __GENERATING_BOUNDS_H
>
> -struct page; /* forward declaration */
> -
> -static inline struct page *compound_head(struct page *page)
> +static inline unsigned long _compound_head(const struct page *page)
> {
> unsigned long head = READ_ONCE(page->compound_head);
>
> if (unlikely(head & 1))
> - return (struct page *) (head - 1);
> - return page;
> + return head - 1;
> + return (unsigned long)page;
> }
>
> +#define compound_head(page) ((typeof(page))_compound_head(page))
> +
> static __always_inline int PageTail(struct page *page)
> {
> return READ_ONCE(page->compound_head) & 1;
>
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
