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[154/192] mm: make compound_head const-preserving

Message ID 20210629024119.KP64mnhwd%akpm@linux-foundation.org (mailing list archive)
State New
Headers show
Series [001/192] mm/gup: fix try_grab_compound_head() race with split_huge_page() | expand

Commit Message

Andrew Morton June 29, 2021, 2:41 a.m. UTC 
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: 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: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/page-flags.h |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
diff mbox series

Patch

--- a/include/linux/page-flags.h~mm-make-compound_head-const-preserving
+++ a/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;