[bug report] RDMA/siw: Fix SQ/RQ drain logic

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Bernard Metzler,

The patch cf049bb31f71: "RDMA/siw: Fix SQ/RQ drain logic" from Oct 4,
2019, leads to the following static checker warning:

	drivers/infiniband/sw/siw/siw_verbs.c:1079 siw_post_receive()
	error: locking inconsistency.  We assume 'read_sem:&qp->state_lock' is both locked and unlocked at the start.

drivers/infiniband/sw/siw/siw_verbs.c
   978  int siw_post_receive(struct ib_qp *base_qp, const struct ib_recv_wr *wr,
   979                       const struct ib_recv_wr **bad_wr)
   980  {
   981          struct siw_qp *qp = to_siw_qp(base_qp);
   982          unsigned long flags;
   983          int rv = 0;
   984  
   985          if (qp->srq) {
   986                  *bad_wr = wr;
   987                  return -EOPNOTSUPP; /* what else from errno.h? */
   988          }
   989          if (!qp->kernel_verbs) {
   990                  siw_dbg_qp(qp, "no kernel post_recv for user mapped sq\n");
   991                  up_read(&qp->state_lock);
                        ^^^^^^^^^^^^^^^^^^^^^^^^
The patch changes the locking so this isn't held here and should be
released.  Should it be held, though?

   992                  *bad_wr = wr;
   993                  return -EINVAL;
   994          }
   995  
   996          /*
   997           * Try to acquire QP state lock. Must be non-blocking
   998           * to accommodate kernel clients needs.
   999           */
  1000          if (!down_read_trylock(&qp->state_lock)) {
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  1001                  if (qp->attrs.state == SIW_QP_STATE_ERROR) {
  1002                          /*
  1003                           * ERROR state is final, so we can be sure
  1004                           * this state will not change as long as the QP
  1005                           * exists.
  1006                           *
  1007                           * This handles an ib_drain_rq() call with
  1008                           * a concurrent request to set the QP state
  1009                           * to ERROR.
  1010                           */
  1011                          rv = siw_rq_flush_wr(qp, wr, bad_wr);
  1012                  } else {

regards,
dan carpenter