Re: [PATCH v1] SUNRPC: Ensure backchannel transports are marked connected

[Trond Myklebust <trondmy@hammerspace.com>]

On Thu, 2021-08-19 at 08:29 -0400, Chuck Lever wrote:
> With NFSv4.1+ on RDMA, backchannel recovery appears not to work.
> 
> xprt_setup_xxx_bc() is invoked by the client's first CREATE_SESSION
> operation, and it always marks the rpc_clnt's transport as
> connected.
> 
> On a subsequent CREATE_SESSION, if rpc_create() is called and
> xpt_bc_xprt is populated, it might not be connected (for instance,
> if a backchannel fault has occurred). Ensure that code path returns
> a connected xprt also.
> 
> Reported-by: Timo Rothenpieler <timo@rothenpieler.org>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/clnt.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index 8b4de70e8ead..570480a649a3 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -535,6 +535,7 @@ struct rpc_clnt *rpc_create(struct
> rpc_create_args *args)
>                 xprt = args->bc_xprt->xpt_bc_xprt;
>                 if (xprt) {
>                         xprt_get(xprt);
> +                       xprt_set_connected(xprt);
>                         return rpc_create_xprt(args, xprt);
>                 }
>         }
> 
> 

No. This is wrong. If the connection got disconnected, then the client
needs to reconnect and build a new connection altogether. We can't just
make pretend that the old connection still exists.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com