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    SubjectPossibly wrong BIO usage in ide_multwrite

    I was just investigating where bio->bi_idx gets modified in the kernel.

    I found these lines in ide-disk.c in ide_multwrite (DMA off, TASKFILE_IO

    > if (++bio->bi_idx >= bio->bi_vcnt) {
    > bio->bi_idx = 0;
    > bio = bio->bi_next;
    > }

    (rq->bio also gets changed but it's protected by the scratch buffer)

    I think changing the bi_idx here is dangerous because
    end_that_request_first needs this value to be unchanged because it
    tracks the progress of the bio processing and updates bi_idx itself.

    And bio->bi_idx = 0 is probably wrong because the bio can be submitted
    with bio->bi_idx > 0 (if the bio was splitted and there are clones that
    share the bio_vec array, like raid or device-mapper code).

    If it really needs to play with bi_idx itself care should be taken to
    reset bi_idx to the original value, not to zero.

    I wasn't able to trigger a problem though, I don't know why exactly,
    perhaps there are paths in __end_that_request_first that are not
    interested in bi_dx. I still think there is something wrong with it.

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      Last update: 2005-03-22 13:59    [W:0.037 / U:26.868 seconds]
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