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    Subject[PATCH] mthca: initialize send and receive queue locks separately
    Date
    mthca: initialize send and receive queue locks separately

    lockdep identifies a lock by the call site of its initialization. By
    initializing the send and receive queue locks in mthca_wq_init() we confuse
    lockdep. It warns that that the ordered acquiry of both locks in
    mthca_modify_qp() is recursive acquiry of one lock:

    =============================================
    [ INFO: possible recursive locking detected ]
    ---------------------------------------------
    modprobe/1192 is trying to acquire lock:
    (&wq->lock){....}, at: [<f892b4db>] mthca_modify_qp+0x60/0xa7b [ib_mthca]
    but task is already holding lock:
    (&wq->lock){....}, at: [<f892b4ce>] mthca_modify_qp+0x53/0xa7b [ib_mthca]

    Initializing the locks separately in mthca_alloc_qp_common() stops the warning
    and will let lockdep enforce proper ordering on paths that acquire both locks.

    Signed-off-by: Zach Brown <zach.brown@oracle.com>
    ---

    drivers/infiniband/hw/mthca/mthca_qp.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    Index: 2.6.17-mm6/drivers/infiniband/hw/mthca/mthca_qp.c
    ===================================================================
    --- 2.6.17-mm6.orig/drivers/infiniband/hw/mthca/mthca_qp.c 2006-07-03 08:41:16.000000000 -0400
    +++ 2.6.17-mm6/drivers/infiniband/hw/mthca/mthca_qp.c 2006-07-03 10:05:52.000000000 -0400
    @@ -224,7 +224,7 @@

    static void mthca_wq_init(struct mthca_wq *wq)
    {
    - spin_lock_init(&wq->lock);
    + /* mthca_alloc_qp_common() initializes the locks */
    wq->next_ind = 0;
    wq->last_comp = wq->max - 1;
    wq->head = 0;
    @@ -1114,6 +1114,9 @@
    qp->sq_policy = send_policy;
    mthca_wq_init(&qp->sq);
    mthca_wq_init(&qp->rq);
    + /* these are initialized separately so lockdep can tell them apart */
    + spin_lock_init(&qp->sq.lock);
    + spin_lock_init(&qp->rq.lock);

    ret = mthca_map_memfree(dev, qp);
    if (ret)
    -
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