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    SubjectRe: [PATCH] fixes for linked list bugs in block I/O code
    On Wed, May 07 2003, Dave Peterson wrote:
    > I found a couple of small linked list bugs in __make_request() in
    > drivers/block/ll_rw_blk.c. The bugs exist in both kernels
    > 2.4.20 and 2.5.69. Therefore I have made patches for both
    > kernels. The problem is that when inserting a new buffer_head
    > into the linked list of buffer_head structures maintained by
    > "struct request", the b_reqnext field is not initialized.
    >
    > -Dave Peterson
    > dsp@llnl.gov
    >
    >
    > ========== START OF 2.4.20 PATCH FOR drivers/block/ll_rw_blk.c ===========
    > --- ll_rw_blk.c.old Wed May 7 15:54:58 2003
    > +++ ll_rw_blk.c.new Wed May 7 15:58:07 2003
    > @@ -973,6 +973,7 @@
    > insert_here = &req->queue;
    > break;
    > }
    > + bh->b_reqnext = req->bhtail->b_reqnext;

    This is convoluted nonsense, bhtail->b_reqnext is NULL by definition. So
    a simple

    bh->b_reqnext = NULL;

    is much clearer.

    > req->bhtail->b_reqnext = bh;
    > req->bhtail = bh;
    > req->nr_sectors = req->hard_nr_sectors += count;
    > @@ -1061,6 +1062,7 @@
    > req->waiting = NULL;
    > req->bh = bh;
    > req->bhtail = bh;
    > + bh->b_reqnext = NULL;
    > req->rq_dev = bh->b_rdev;
    > req->start_time = jiffies;
    > req_new_io(req, 0, count);

    Bart already covered why 2.5 definitely does not need it. I dunno what
    to say for 2.4, to me it looks like a BUG if you pass in a buffer_head
    with uninitialized b_reqnext. Why should that member be any different?

    In fact, from where did you see this buffer_head coming from? Who is
    submitting IO on a not properly inited bh? To me, that sounds like not a
    block layer bug but an fs bug.

    --
    Jens Axboe

    -
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