• Michal Hocko's avatar
    mm: fix do_pages_move status handling · 8f175cf5
    Michal Hocko authored
    Li Wang has reported that LTP move_pages04 test fails with the current
    tree:
    
    LTP move_pages04:
       TFAIL  :  move_pages04.c:143: status[1] is EPERM, expected EFAULT
    
    The test allocates an array of two pages, one is present while the other
    is not (resp.  backed by zero page) and it expects EFAULT for the second
    page as the man page suggests.  We are reporting EPERM which doesn't make
    any sense and this is a result of a bug from cf5f16b23ec9 ("mm: unclutter
    THP migration").
    
    do_pages_move tries to handle as many pages in one batch as possible so we
    queue all pages with the same node target together and that corresponds to
    [start, i] range which is then used to update status array.
    add_page_for_migration will correctly notice the zero (resp.  !present)
    page and returns with EFAULT which gets written to the status.  But if
    this is the last page in the array we do not update start and so the last
    store_status after the loop will overwrite the range of the last batch
    with NUMA_NO_NODE (which corresponds to EPERM).
    
    Fix this by simply bailing out from the last flush if the pagelist is
    empty as there is clearly nothing more to do.
    
    Link: http://lkml.kernel.org/r/20180418121255.334-1-mhocko@kernel.org
    Fixes: cf5f16b23ec9 ("mm: unclutter THP migration")
    Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
    Reported-by: default avatarLi Wang <liwang@redhat.com>
    Tested-by: default avatarLi Wang <liwang@redhat.com>
    Cc: Zi Yan <zi.yan@cs.rutgers.edu>
    Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    8f175cf5
migrate.c 77.5 KB