Re: [PATCH] svcrdma: disable timeouts on rdma backchannel

[bfields@fieldses.org (J. Bruce Fields)]

On Wed, Feb 24, 2021 at 02:18:18PM +0000, Chuck Lever wrote:
> 
> 
> > On Feb 22, 2021, at 6:36 PM, Timo Rothenpieler <timo@rothenpieler.org> wrote:
> > 
> > This brings it in line with the regular tcp backchannel, which also has
> > all those timeouts disabled.
> > 
> > Prevents the backchannel from timing out, getting some async operations
> > like server side copying getting stuck indefinitely on the client side.
> > 
> > Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
> 
> Thanks for your patch! I've included it in the for-rc branch at
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git

So, I'm sure this patch makes sense.

But I'm also curious why it's not recovering.

What I think should happen:

	- clp->cl_cb_state should be set to NFSD4_CB_DOWN.
	- This should cause the next SEQUENCE reply to have
	  SEQ4_STATUS_CB_PATH_DOWN set.
	- That should poke the client to recover.  (Maybe by sending a
	  BIND_CONN_TO_SESSION call?)

I'd be curious whether any of that's actually happening.

--b.

> 
> 
> > ---
> > Did the same testing with this applied than before, and could not
> > observe it getting stuck, same as with the previous patch, which I
> > removed before testing this one.
> > 
> > This obviously still does not fix the issue of it being seemingly unable
> > to reestablish the disconnected backchannel.
> > An event that disconnects the backchannel but leaves the main connection
> > intact seems a pretty rare occurance though, outside of this issue.
> > 
> > net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > index 63f8be974df2..8186ab6f99f1 100644
> > --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> > @@ -252,9 +252,9 @@ xprt_setup_rdma_bc(struct xprt_create *args)
> > 	xprt->timeout = &xprt_rdma_bc_timeout;
> > 	xprt_set_bound(xprt);
> > 	xprt_set_connected(xprt);
> > -	xprt->bind_timeout = RPCRDMA_BIND_TO;
> > -	xprt->reestablish_timeout = RPCRDMA_INIT_REEST_TO;
> > -	xprt->idle_timeout = RPCRDMA_IDLE_DISC_TO;
> > +	xprt->bind_timeout = 0;
> > +	xprt->reestablish_timeout = 0;
> > +	xprt->idle_timeout = 0;
> > 
> > 	xprt->prot = XPRT_TRANSPORT_BC_RDMA;
> > 	xprt->ops = &xprt_rdma_bc_procs;
> > -- 
> > 2.25.1
> > 
> 
> --
> Chuck Lever
> 
>