RDS: avoid double destory of cm_id when rdms_resolve_route fails

RDS: avoid double destory of cm_id when rdms_resolve_route fails

It crashes in rds_ib_conn_shutdown because it was using a freed cm_id.  The
cm_id had got freed quite a while back actually (more than 15 secs back) during
an earlier connect attempt.

This was the sequence of the earlier connect attempt: rds_ib_conn_connect calls
rdma_resolve_addr.  The synchronous part of rdma_resolve_addr succeeds. But the
asynchronous part fails at some point.  RDMA Connection Manager returns the
event RDMA_CM_EVENT_ADDR_RESOLVED. This part succeeds.  Next, RDS calls
rdma_resolve_route from the rds_rdma_cm_event_handler. This fails.  We return
this error back to the RDMA CM addr_handler which destroys the cm_id as
follows: addr_handler (cma.c):

static void addr_handler(int status, struct sockaddr *src_addr,
                         struct rdma_dev_addr *dev_addr, void *context)
{
     .....
        if (id_priv->id.event_handler(&id_priv->id, &event)) {
                cma_exch(id_priv, CMA_DESTROYING);
                mutex_unlock(&id_priv->handler_mutex);
                cma_deref_id(id_priv);
                rdma_destroy_id(&id_priv->id);    <----  here
                return;
        }

RDS continues to point to this freed cm_id.

Later when a new connect req comes in from the remote side, we shutdown this cm_id
and try to reconnect:
  /*
   * after 15 seconds, give up on existing connection
   * attempts and make them try again.  At this point
   * it's no longer a race but something has gone
   * horribly wrong
   */
   if (now > conn->c_connection_start &&
           now - conn->c_connection_start > 5) {
              printk(KERN_CRIT "rds connection racing for 15s, forcing reset "
                        "connection %u.%u.%u.%u->%u.%u.%u.%u\n",
                        NIPQUAD(conn->c_laddr), NIPQUAD(conn->c_faddr));
       rds_conn_drop(conn);
          ....
We crash during the shutdown.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Bang Nguyen <bang.nguyen@oracle.com>