Re: [PATCH 3/9] IB: add a helper to safely drain a QP

[Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx>]

> That won't work for iWARP.  Is this code new?  I didn't see any errors that would result from this code when I tested iSER over
> cxgb4 with the old iwarp support patches.

Steve,

I think I figured out why this works with iWARP.

For iWARP, rdma_disconnect() calls iw_cm_disconnect() with abrupt=0
which would make iw_cm_disconnect() move the QP into SQ_DRAIN state"

int iw_cm_disconnect(struct iw_cm_id *cm_id, int abrupt)
{
	...

        if (qp) {
                if (abrupt)
                        ret = iwcm_modify_qp_err(qp);
                else
                        ret = iwcm_modify_qp_sqd(qp);

                /*
                 * If both sides are disconnecting the QP could
                 * already be in ERR or SQD states
                 */
                ret = 0;
	}
}

IFAIK, SQD state allows the ULP to post work requests on the send
queue and expect these work requests to FLUSH.

So Maybe we should have:
void ib_drain_qp(struct ib_qp *qp)
{
    struct ib_qp_attr attr = { };
    struct ib_stop_cqe rstop, sstop;
    struct ib_recv_wr rwr = {}, *bad_rwr;
    struct ib_send_wr swr = {}, *bad_swr;
    enum ib_qp_state state;
    int ret;

    if rdma_cap_ib_cm(id->device, id->port_num) {
	state = IB_QPS_ERR;
    else if rdma_cap_iw_cm(id->device, id->port_num)
        state = IB_QPS_SQD;
    else
       return;

    rwr.wr_cqe = &rstop.cqe;
    rstop.cqe.done = ib_stop_done;
    init_completion(&rstop.done);

    swr.wr_cqe = &sstop.cqe;
    sstop.cqe.done = ib_stop_done;
    swr.send_flags = IB_SEND_SIGNALED;
    init_completion(&sstop.done);

    attr.qp_state = state;
    ret = ib_modify_qp(qp, &attr, IB_QP_STATE);
    if (ret) {
        WARN_ONCE(ret, "failed to drain QP: %d\n", ret);
        return;
    }

    ret = ib_post_recv(qp, &rwr, &bad_rwr);
    if (ret) {
        WARN_ONCE(ret, "failed to drain recv queue: %d\n", ret);
        return;
    }

    ret = ib_post_send(qp, &swr, &bad_swr);
    if (ret) {
        WARN_ONCE(ret, "failed to drain send queue: %d\n", ret);
        return;
    }

    wait_for_completion(&rstop.done);
    wait_for_completion(&sstop.done);
}

Thoughts?
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