Re: RDMA subsystem namespace related questions (was Re: Finding the namespace of a struct ib_device)

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Oct 09, 2020 at 10:48:55AM -0400, Chuck Lever wrote:
> Hi Jason-
> 
> > On Oct 9, 2020, at 10:39 AM, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > 
> > On Fri, Oct 09, 2020 at 12:49:30PM +0800, Ka-Cheong Poon wrote:
> >> As I mentioned before, this is a very serious restriction on how
> >> the RDMA subsystem can be used in a namespace environment by kernel
> >> module.  The reason given for this restriction is that any kernel
> >> socket without a corresponding user space file descriptor is "rogue".
> >> All Internet protocol code create a kernel socket without user
> >> interaction.  Are they all "rogue"?
> > 
> > You should work with Chuck to make NFS use namespaces properly and
> > then you can propose what changes might be needed with a proper
> > justification.
> 
> The NFS server code already uses namespaces for creating listener
> endpoints, already has a user space component that drives the
> creation of listeners, and already passes an appropriate struct
> net to rdma_create_id. As far as I am aware, it is namespace-aware
> and -friendly all the way down to rdma_create_id().
> 
> What more needs to be done?

I have no idea, if you are able to pass a namespace all the way down
to the listening cm_id and everything works right (I'm skeptical) then
there is nothing more to worry about - why are we having this thread?

> > The rules for lifetime on IB clients are tricky, and the interaction
> > with namespaces makes it all a lot more murky.
> 
> I think what Ka-cheong is asking is for a detailed explanation of
> these lifetime rules so we can understand why rdma_create_id bumps
> the namespace reference count.

It is because the CM has no code to revoke a CM ID before the
namespace goes away and the pointer becomes invalid.

Jason