Sean Hefty wrote:
Is the issue 6f8372b6 ("RDMA/cm: fix loopback address support")? This just went in for 2.6.33, which is still at -rc6, so if we can quickly reach a consensus, there is still time to get a fix in for 2.6.33.That should be the patch in question. I'm not sure about reaching consensus. :) If the other changes to the rdma_cm aren't closely tied to that change, we may be able to back that one patch out until we can get whatever other fix may be needed.
I'd like to do this approach. Then re-submit once we come to consensus...
In my view, openmpi has a bug in that it can pass a loopback address to a remote peer and expect it to be used to establish a connection. Steve seems to agree with this. My original intent was to allow the use of the loopback address with the rdma_cm. I.e. 127.0.0.1 meant 'this host', and not 'software loopback'. I just had Arlin run a quick test with OFED 1.4 over IB, and it allows binding to 127.0.0.1, but never forms connections. I.e. ucmatose -b 127.0.0.1 succeeds in listening, but ucmatose -s 127.0.0.1 fails to connect because of a route error. (Hmm... I'm still confused about what openmpi is doing then.)
But it must fail in OFED-1.4 if binding to an iwarp interface. Maybe there was IB-only logic allowing 127.0.0.1 binds in OFED-1.4? The reason openmpi might still work on IB is that its not typical to use the rdma-cm for IB setups. Its required for iwarp though.
Jeff, what's the default CPC for IB devices?
Even if an application were to use non-loopback IP addresses, there's no guarantee of forming a connection if those addresses map to an iwarp device. So, even if the rdma_cm fails binding to 127.0.0.1 unless there's some RDMA device (software or hardware - not sure why we care) capable of supporting it, an application would need to also deal with failures from rdma_resolve_addr. Indicating loopback through a device capability flag seems like the right approach, and the rdma_cm can use this to fail rdma_bind_addr/rdma_resolve_addr calls. That's probably not a trivial patch however. - Sean
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