• Jan Kara's avatar
    mm: fix XFS oops due to dirty pages without buffers on s390 · ef5d437f
    Jan Kara authored
    On s390 any write to a page (even from kernel itself) sets architecture
    specific page dirty bit.  Thus when a page is written to via buffered
    write, HW dirty bit gets set and when we later map and unmap the page,
    page_remove_rmap() finds the dirty bit and calls set_page_dirty().
    Dirtying of a page which shouldn't be dirty can cause all sorts of
    problems to filesystems.  The bug we observed in practice is that
    buffers from the page get freed, so when the page gets later marked as
    dirty and writeback writes it, XFS crashes due to an assertion
    BUG_ON(!PagePrivate(page)) in page_buffers() called from
    Similar problem can also happen when zero_user_segment() call from
    xfs_vm_writepage() (or block_write_full_page() for that matter) set the
    hardware dirty bit during writeback, later buffers get freed, and then
    page unmapped.
    Fix the issue by ignoring s390 HW dirty bit for page cache pages of
    mappings with mapping_cap_account_dirty().  This is safe because for
    such mappings when a page gets marked as writeable in PTE it is also
    marked dirty in do_wp_page() or do_page_fault().  When the dirty bit is
    cleared by clear_page_dirty_for_io(), the page gets writeprotected in
    page_mkclean().  So pagecache page is writeable if and only if it is
    Thanks to Hugh Dickins for pointing out mapping has to have
    mapping_cap_account_dirty() for things to work and proposing a cleaned
    up variant of the patch.
    The patch has survived about two hours of running fsx-linux on tmpfs
    while heavily swapping and several days of running on out build machines
    where the original problem was triggered.
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: <stable@vger.kernel.org>		[3.0+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
rmap.c 51.3 KB