• Hugh Dickins's avatar
    mm/memory.c: use entry = ACCESS_ONCE(*pte) in handle_pte_fault() · c0d73261
    Hugh Dickins authored
    Use ACCESS_ONCE() in handle_pte_fault() when getting the entry or
    orig_pte upon which all subsequent decisions and pte_same() tests will
    be made.
    
    I have no evidence that its lack is responsible for the mm/filemap.c:202
    BUG_ON(page_mapped(page)) in __delete_from_page_cache() found by
    trinity, and I am not optimistic that it will fix it.  But I have found
    no other explanation, and ACCESS_ONCE() here will surely not hurt.
    
    If gcc does re-access the pte before passing it down, then that would be
    disastrous for correct page fault handling, and certainly could explain
    the page_mapped() BUGs seen (concurrent fault causing page to be mapped
    in a second time on top of itself: mapcount 2 for a single pte).
    Signed-off-by: default avatarHugh Dickins <hughd@google.com>
    Cc: Sasha Levin <sasha.levin@oracle.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Konstantin Khlebnikov <koct9i@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    c0d73261
memory.c 102 KB