diff options
| author | Andrea Arcangeli <aarcange@redhat.com> | 2011-03-18 00:16:35 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-03-27 11:35:58 -0700 |
| commit | 582d8b9e2879512507b8a9409f85fb1394e1c53e (patch) | |
| tree | 54c34e9e80ba524daff7ae6a44673eb55bff6ba9 /include | |
| parent | b62a6839fdf5cb733559164da4f5242ab6de8e06 (diff) | |
mm: PageBuddy and mapcount robustness
commit ef2b4b95a63a1d23958dcb99eb2c6898eddc87d0 upstream.
Change the _mapcount value indicating PageBuddy from -2 to -128 for
more robusteness against page_mapcount() undeflows.
Use reset_page_mapcount instead of __ClearPageBuddy in bad_page to
ignore the previous retval of PageBuddy().
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mm.h | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index f6385fc17ad4..c67adb4ea5eb 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -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) |