CM REQs cannot be successfully retried, because a new pv_cm_id is
created for each request, without checking if one already exists.
By checking if an id exists before creating one, the bug is fixed.
This bug can be provoked by running an RDMA CM user-land application,
but inserting a five seconds delay before the rdma_accept() call on
the passive side. This delay is larger than the default CMA timeout,
and triggers a retry from the active side. The retried REQ will use
another pv_cm_id (the cm_id on the wire). This confuses the CM
protocol and two REJs are sent from the passive side.
Here is an excerpt from ibdump running without the patch: