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    SubjectRe: 2.6.5-rc1-mm2 and direct_read_under and wb
    On Mon, 2004-03-22 at 13:23, Chris Mason wrote:
    > On Mon, 2004-03-22 at 13:10, Daniel McNeil wrote:
    > > Andrew and Chris,
    > >
    > > I re-ran the direct_read_under tests over the weekend on ext3 with
    > > the attached wb_rwsema patch and ran without errors.
    > >
    > > It looks like the same thing as before -- async writebacks are causing
    > > the sync writebacks to miss pages.
    > >
    > > Thoughts?
    > It does seem clear that's what is happening, but the part I don't
    > understand is exactly where they are racing.

    Wait, maybe I do see it.

    In __block_write_full_page, if the buffers are locked by ll_rw_block and
    under io, they are clean. The page is only redirtied in this case
    because the buffers are clean.

    So we set_page_writeback and nr_underway == 0. Then, in the if
    (nr_underway == 0) code, we clear page writeback even though the buffers
    are still locked and under io.


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