mm: add VM_BUG_ON_PAGE() to page_mapcount()

Add VM_BUG_ON_PAGE() for slab pages. _mapcount is an union with slab struct in struct page, so we must avoid accessing _mapcount if this page is a slab page. Also remove the unneeded bracket. Signed-off-by: Yalin Wang <[email protected]> Acked-by: Kirill A. Shutemov <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
nathanchance · Feb 12, 2015 · 1d148e2 · 1d148e2
1 parent e4b294c
commit 1d148e2
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/include/linux/mm.h b/include/linux/mm.h
@@ -484,7 +484,8 @@ static inline void page_mapcount_reset(struct page *page)
 
 static inline int page_mapcount(struct page *page)
 {
-	return atomic_read(&(page)->_mapcount) + 1;
+	VM_BUG_ON_PAGE(PageSlab(page), page);
+	return atomic_read(&page->_mapcount) + 1;
 }
 
 static inline int page_count(struct page *page)