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    SubjectRe: 2.6.18 ext3 panic.
    On Wed, 2006-10-11 at 16:22 +0200, Jan Kara wrote:
    > > Jan Kara wrote:
    > >
    > > > Umm, but these two traces confuse me:
    > > >1) They are different traces that those you wrote about initially,
    > > >aren't they? Because here we would not call sync_dirty_buffer() from
    > > >journal_dirty_data().
    > > > BTW: Does this buffer trace lead to that Oops in submit_bh()? I guess not
    > > >as the buffer is not dirty...
    > >
    > > They do wind up at the same oops, from the same "testcase" (i.e. beat the
    > > tar out of the filesystem with multiple fsx's and fsstress...)
    > >
    > > The buffer is not dirty at that tracepoint because it has just done
    > > if (locked && test_clear_buffer_dirty(bh)) {
    > > prior to the tracepoint...
    > Oh, I see. OK.
    > >
    > > See the whole traces at
    > >
    > >
    > >
    > Hmm, those traces look really useful. I just have to digest them ;).
    > > As an aside, when we do journal_unmap_buffer... should it stay on
    > > t_sync_datalist?
    > Yes, it should and it seems it really was removed from it at some
    > point. Only later journal_dirty_data() came and filed it back to the
    > BJ_SyncData list. And the buffer remained unmapped till the commit time
    > and then *bang*... It may even be a race in ext3 itself that it called
    > journal_dirty_data() on an unmapped buffer but I have to read some more
    > code.

    Yes. calling journal_dirty_data() on unmapped buffer can definitely
    happen. (only thing i am not sure is - why doesn't happen with a
    simple testcase like dirtying only a part of a page in 1k filesystem.
    I am not sure why we need journal_unmap_buffer() in the sequence).

    Here is what I think is happening..

    journal_unmap_buffer() - cleaned the buffer, since its outside EOF, but
    its a part of the same page. So it remained on the page->buffers
    list. (at this time its not part of any transaction).

    Then, ordererd_commit_write() called journal_dirty_data() and we added
    all these buffers to BJ_SyncData list. (at this time buffer is clean -
    not dirty).

    Now msync() called __set_page_dirty_buffers() and dirtied *all* the
    buffers attached to this page.

    journal_submit_data_buffers() got around to this buffer and tried to
    submit the buffer...

    Andrew is right - only option for us to check the filesize in the
    write out path and skip the buffers beyond EOF.


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