RE: [PATCH V1] NFS-RDMA: fix qp pointer validation checks

[Devesh Sharma <Devesh.Sharma-iH1Dq9VlAzfQT0dZR+AlfA@public.gmane.org>]

Hi Chuck

> -----Original Message-----
> From: Chuck Lever [mailto:chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org]
> Sent: Tuesday, April 15, 2014 2:24 AM
> To: Devesh Sharma
> Cc: Linux NFS Mailing List; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; Trond Myklebust
> Subject: Re: [PATCH V1] NFS-RDMA: fix qp pointer validation checks
> 
> Hi Devesh-
> 
> 
> On Apr 13, 2014, at 12:01 AM, Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote:
> 
> >
> > On Apr 11, 2014, at 7:51 PM, Devesh Sharma
> <Devesh.Sharma-iH1Dq9VlAzfQT0dZR+AlfA@public.gmane.org> wrote:
> >
> >> Hi  Chuck,
> >> Yes that is the case, Following is the trace I got.
> >>
> >> <4>RPC:   355 setting alarm for 60000 ms
> >> <4>RPC:   355 sync task going to sleep
> >> <4>RPC:       xprt_rdma_connect_worker: reconnect
> >> <4>RPC:       rpcrdma_ep_disconnect: rdma_disconnect -1
> >> <4>RPC:       rpcrdma_ep_connect: rpcrdma_ep_disconnect status -1
> >> <3>ocrdma_mbx_create_qp(0) rq_err
> >> <3>ocrdma_mbx_create_qp(0) sq_err
> >> <3>ocrdma_create_qp(0) error=-1
> >> <4>RPC:       rpcrdma_ep_connect: rdma_create_qp failed -1
> >> <4>RPC:   355 __rpc_wake_up_task (now 4296956756)
> >> <4>RPC:   355 disabling timer
> >> <4>RPC:   355 removed from queue ffff880454578258 "xprt_pending"
> >> <4>RPC:       __rpc_wake_up_task done
> >> <4>RPC:       xprt_rdma_connect_worker: exit
> >> <4>RPC:   355 sync task resuming
> >> <4>RPC:   355 xprt_connect_status: error 1 connecting to server
> 192.168.1.1
> >
> > xprtrdma's connect worker is returning "1" instead of a negative errno.
> > That's the bug that triggers this chain of events.
> 
> rdma_create_qp() has returned -EPERM. There's very little xprtrdma can do
> if the provider won't even create a QP. That seems like a rare and fatal
> problem.
> 
> For the moment, I'm inclined to think that a panic is correct behavior, since
> there are outstanding registered memory regions that cannot be cleaned up
> without a QP (see below).
Well, I think the system should still remain alive. This will definatly cause a memory leak. But QP create failure does not mean system should also crash.
I think for the time being it is worth to put Null pointer checks to prevent system from crash.

> 
> 
> > RPC tasks waiting for the reconnect are awoken. xprt_connect_status()
> > doesn't recognize a tk_status of "1", so it turns it into -EIO, and
> > kills each waiting RPC task.
> 
> >> <4>RPC:       wake_up_next(ffff880454578190 "xprt_sending")
> >> <4>RPC:   355 call_connect_status (status -5)
> >> <4>RPC:   355 return 0, status -5
> >> <4>RPC:   355 release task
> >> <4>RPC:       wake_up_next(ffff880454578190 "xprt_sending")
> >> <4>RPC:       xprt_rdma_free: called on 0x(null)
> >
> > And as part of exiting, the RPC task has to free its buffer.
> >
> > Not exactly sure why req->rl_nchunks is not zero for an NFSv4 GETATTR.
> > This is why rpcrdma_deregister_external() is invoked here.
> >
> > Eventually this gets around to attempting to post a LOCAL_INV WR with
> > ->qp set to NULL, and the panic below occurs.
> 
> This is a somewhat different problem.
> 
> Not only do we need to have a good ->qp here, but it has to be connected
> and in the ready-to-send state before LOCAL_INV work requests can be
> posted.
> 
> The implication of this is that if a server disconnects (server crash or network
> partition), the client is stuck waiting for the server to come back before it can
> deregister memory and retire outstanding RPC requests.
This is a real problem to solve. In the existing state of xprtrdma code. Even a Server reboot will cause
Client to crash.
> 
> This is bad for ^C or soft timeouts or umount ... when the server is
> unavailable.
> 
> So I feel we need better clean-up when the client cannot reconnect.
Unreg old frmrs with the help of new QP? Until the new QP is created with same PD and FRMR is bound to PD and not to QP.
> Probably deregistering RPC chunk MR's before finally tearing down the old
> QP is what is necessary.

We need a scheme that handles Memory registrations separately from connection establishment and do book-keeping of which region is Registered and which one is not.
Once the new connection is back. Either start using old mem-regions as it is, or invalidate old and re-register on the new QP.
What is the existing scheme xprtrdma is following? Is it the same?

I think it is possible to create FRMR on qp->qp_num = x while invalidate on qp->qp_num = y until qpx.pd == qpy.pd
> 
> I'll play around with this idea.
> 
> 
> --
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
> 
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html