Re: [PATCH rdma-rc 3/9] Revert "RDMA/cma: Simplify rdma_resolve_addr() error flow"

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Feb 14, 2020 at 03:11:48AM +0000, Parav Pandit wrote:
> On 2/13/2020 7:30 AM, Jason Gunthorpe wrote:
> > On Wed, Feb 12, 2020 at 09:26:29AM +0200, Leon Romanovsky wrote:
> >> From: Parav Pandit <parav@mellanox.com>
> >>
> >> This reverts commit 219d2e9dfda9431b808c28d5efc74b404b95b638.
> >>
> >> Below flow requires cm_id_priv's destination address to be setup
> >> before performing rdma_bind_addr().
> >> Without which, source port allocation for existing bind list fails
> >> when port range is small, resulting into rdma_resolve_addr()
> >> failure.
> > 
> > I don't quite understands this - what is "when port range is small" ?
> >  
> There is sysfs knob to reduce source port range to use for binding.
> So it is easy to create the issue by reducing port range to handful of them.
> 
> >> rdma_resolve_addr()
> >>   cma_bind_addr()
> >>     rdma_bind_addr()
> >>       cma_get_port()
> >>         cma_alloc_any_port()
> >>           cma_port_is_unique() <- compared with zero daddr
> > 
> > Do you understand why cma_port_is_unique is even testing the dst_addr?
> > It seems very strange.
> 
> ma_port_unique() reuses the source port as long as
> destination is different (destination = either different
> dest.addr or different dest.port between two cm_ids ).
> 
> This behavior is synonymous to TCP also.
> 
> > Outbound connections should not alias the source port in the first
> > place??
> >
> I believe it can because TCP seems to allow that too as long destination
> is different.
> 
> I think it allows if it results into different 4-tuple.

So the issue here is if the dest is left as 0 then the
cma_alloc_any_port() isn't able to alias source ports any more?

Jason