Commit 0f2317e3 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Linus Torvalds
Browse files

mm: make compound_head const-preserving 

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.

Link: https://lkml.kernel.org/r/20210416231531.2521383-5-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: default avatarWilliam Kucharski <william.kucharski@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8bf6f451

include/linux/page-flags.h

+5 −5
Original line number Diff line number Diff line
@@ -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;