mm: PageBuddy and mapcount robustness 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 <[email protected]> Reported-by: Hugh Dickins <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>