• Hugh Dickins's avatar
    mm: thp: refix false positive BUG in page_move_anon_rmap() · 5a49973d
    Hugh Dickins authored
    The VM_BUG_ON_PAGE in page_move_anon_rmap() is more trouble than it's
    worth: the syzkaller fuzzer hit it again.  It's still wrong for some THP
    cases, because linear_page_index() was never intended to apply to
    addresses before the start of a vma.
    
    That's easily fixed with a signed long cast inside linear_page_index();
    and Dmitry has tested such a patch, to verify the false positive.  But
    why extend linear_page_index() just for this case? when the avoidance in
    page_move_anon_rmap() has already grown ugly, and there's no reason for
    the check at all (nothing else there is using address or index).
    
    Remove address arg from page_move_anon_rmap(), remove VM_BUG_ON_PAGE,
    remove CONFIG_DEBUG_VM PageTransHuge adjustment.
    
    And one more thing: should the compound_head(page) be done inside or
    outside page_move_anon_rmap()? It's usually pushed down to the lowest
    level nowadays (and mm/memory.c shows no other explicit use of it), so I
    think it's better done in page_move_anon_rmap() than by caller.
    
    Fixes: 0798d3c0 ("mm: thp: avoid false positive VM_BUG_ON_PAGE in page_move_anon_rmap()")
    Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1607120444540.12528@eggly.anvilsSigned-off-by: default avatarHugh Dickins <hughd@google.com>
    Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
    Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: <stable@vger.kernel.org>	[4.5+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    5a49973d
memory.c 107 KB