Freeing QN=1 State

When does draft-ietf-rddp-rdmap-02.txt consider an inbound RDMA Read 
Request Message finished such that the state associated with QN=1 (the 
IRRQ) for the RDMA Read Request can be freed?

Put another way, if IRRQ is 1 (for simplicity), when is it legal for a 
new RDMA Read Request to be received?  Is it:

a) Once the RDMA Read Response Message has been given to DDP?
b) Once the RDMA Read Response Message has been "acked" by the data sink?
c) up to the implementation?
d) specified somewhere that I just missed?

Using (a) as a solution I ran into a DoS problem.  The data sink keeps 
issuing RDMA Read Requests but the LLP window advertised by the data 
sink is so small (or closed) that the resources I believe the IRD 
negotiation was meant to protect actually get depleted.

A compliant sender should not send the next RDMA Read Request until a 
prior one has completed.  However, is the draft assuming a non malicious 
sender?  Personally, I prefer to protect my resources regardless.

I can't find supporting text in the draft for (b).   Doing (c) allows 
for (a) so is the same problem IMHO.

Thanks,
MikeC