Fix barrier fail detection in XFS

[Leann Ogasawara]

SRU Justification: This patch has been accepted into the upstream 2.6.27.2 stable kernel.
It should be pulled into the Ubuntu kernel as well.

TEST CASE: TBD

commit 769b0455c1ec257b9e5067129accab1a6052de4c
Author: Christoph Hellwig <email address hidden>
Date: Fri Oct 10 17:28:29 2008 +1100

    Fix barrier fail detection in XFS

    commit 73f6aa4d44ab6157badc456ddfa05b31e58de5f0 upstream.

    Currently we disable barriers as soon as we get a buffer in xlog_iodone
    that has the XBF_ORDERED flag cleared. But this can be the case not only
    for buffers where the barrier failed, but also the first buffer of a
    split log write in case of a log wraparound. Due to the disabled
    barriers we can easily get directory corruption on unclean shutdowns.
    So instead of using this check add a new buffer flag for failed barrier
    writes.

    This is a regression vs 2.6.26 caused by patch to use the right macro
    to check for the ORDERED flag, as we previously got true returned for
    every buffer.

    Thanks to Toei Rei for reporting the bug.

    Signed-off-by: Christoph Hellwig <email address hidden>
    Reviewed-by: Eric Sandeen <email address hidden>
    Reviewed-by: David Chinner <email address hidden>
    Signed-off-by: Tim Shimmin <email address hidden>
    Signed-off-by: Linus Torvalds <email address hidden>
    Signed-off-by: Greg Kroah-Hartman <email address hidden>