mm: PageBuddy and mapcount robustness (ef2b4b95) · Commits · 戴 / test

include/linux/mm.h

+9 −2

Original line number	Diff line number	Diff line
		@@ -402,16 +402,23 @@ static inline void init_page_count(struct page *page)
		/*
		* PageBuddy() indicate that the page is free and in the buddy system
		* (see mm/page_alloc.c).
		*
		* PAGE_BUDDY_MAPCOUNT_VALUE must be <= -2 but better not too close to
		* -2 so that an underflow of the page_mapcount() won't be mistaken
		* for a genuine PAGE_BUDDY_MAPCOUNT_VALUE. -128 can be created very
		* efficiently by most CPU architectures.
		*/
		#define PAGE_BUDDY_MAPCOUNT_VALUE (-128)

		static inline int PageBuddy(struct page *page)
		{
		return atomic_read(&page->_mapcount) == -2;
		return atomic_read(&page->_mapcount) == PAGE_BUDDY_MAPCOUNT_VALUE;
		}

		static inline void __SetPageBuddy(struct page *page)
		{
		VM_BUG_ON(atomic_read(&page->_mapcount) != -1);
		atomic_set(&page->_mapcount, -2);
		atomic_set(&page->_mapcount, PAGE_BUDDY_MAPCOUNT_VALUE);
		}

		static inline void __ClearPageBuddy(struct page *page)

+2 −2

Original line number	Diff line number	Diff line
		@@ -286,7 +286,7 @@ static void bad_page(struct page *page)

		/* Don't complain about poisoned pages */
		if (PageHWPoison(page)) {
		__ClearPageBuddy(page);
		reset_page_mapcount(page); /* remove PageBuddy */
		return;
		}

		@@ -317,7 +317,7 @@ static void bad_page(struct page *page)
		dump_stack();
		out:
		/* Leave bad fields for debug, except PageBuddy could make trouble */
		__ClearPageBuddy(page);
		reset_page_mapcount(page); /* remove PageBuddy */
		add_taint(TAINT_BAD_PAGE);
		}