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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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 changed files with 5 additions and 5 deletions
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@ -177,17 +177,17 @@ enum pageflags {
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#ifndef __GENERATING_BOUNDS_H
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struct page; /* forward declaration */
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static inline struct page *compound_head(struct page *page)
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static inline unsigned long _compound_head(const struct page *page)
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{
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unsigned long head = READ_ONCE(page->compound_head);
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if (unlikely(head & 1))
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return (struct page *) (head - 1);
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return page;
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return head - 1;
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return (unsigned long)page;
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}
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#define compound_head(page) ((typeof(page))_compound_head(page))
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static __always_inline int PageTail(struct page *page)
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{
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return READ_ONCE(page->compound_head) & 1;
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