[ewg] RE: [ofa-general] [PATCH] ib_ipoib: fix race detaching from mcast group before attaching

[Sean Hefty]

>What's the theory here?  It's not obvious why moving the call to
>ib_sa_free_multicast() fixes the race...

The attach QP only occurs in the context of the multicast callback thread.
ib_sa_free_multicast() blocks until the callback returns, which ensures that the
detach check/call (which is now done after ib_sa_free_multicast) cannot race
with the attach call.

- Sean