Comment 16 for bug 420423

okay, the error is coming from here:

bool blk_do_ordered(struct request_queue *q, struct request **rqp)
{
        struct request *rq = *rqp;
        const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);

        if (!q->ordseq) {
                if (!is_barrier)
                        return true;

                if (q->next_ordered != QUEUE_ORDERED_NONE)
                        return start_ordered(q, rqp);
                else {
                        /*
                         * Queue ordering not supported. Terminate
                         * with prejudice.
                         */
                        blk_dequeue_request(rq);
                        __blk_end_request_all(rq, -EOPNOTSUPP);

partial stack trace:

 [<ffffffff81254768>] blk_update_request+0xca/0x363
 [<ffffffff8127bc00>] ? debug_object_deactivate+0x47/0xf2
 [<ffffffff81254a30>] blk_update_bidi_request+0x2f/0x7f
 [<ffffffff812565b2>] __blk_end_request_all+0x44/0x74
 [<ffffffff8125c096>] blk_do_ordered+0x1e0/0x2ae
 [<ffffffff81256756>] blk_peek_request+0x174/0x1c8
 [<ffffffffa00102d3>] do_virtblk_request+0x192/0x1d3 [virtio_blk]
 [<ffffffff8125710f>] __blk_run_queue+0x54/0x9a