RE: [PATCH v1 05/13] xprtrdma: Don't drain CQs on transport disconnect

Steve Wise
2014-07-02T19:50:32Z

> -----Original Message-----
> From: Devesh Sharma [mailto:Devesh.Sharma-iH1Dq9VlAzfQT0dZR+AlfA@public.gmane.org]
> Sent: Wednesday, July 02, 2014 2:43 PM
> To: Steve Wise; Chuck Lever; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; linux-nfs@vger.kernel.org
> Subject: RE: [PATCH v1 05/13] xprtrdma: Don't drain CQs on transport disconnect
>
> > -----Original Message-----
> > From: Steve Wise [mailto:swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org]
> > Sent: Thursday, July 03, 2014 12:59 AM
> > To: Devesh Sharma; Chuck Lever; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; linux-
> > nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > Subject: Re: [PATCH v1 05/13] xprtrdma: Don't drain CQs on transport
> > disconnect
> >
> > On 7/2/2014 2:06 PM, Devesh Sharma wrote:
> > > This change is very much prone to generate poll_cq errors because of
> > > un-cleaned completions which still point to the non-existent QPs. On
> > > the new connection when these completions are polled, the poll_cq will fail
> > because old QP pointer is already NULL.
> > > Did anyone hit this situation during their testing?
> >
> > Hey Devesh,
> >
> > iw_cxgb4 will silently toss CQEs if the QP is not active.
>
> Ya, just now checked that in mlx and cxgb4 driver code. On the other hand ocrdma is asserting
> a BUG-ON for such CQEs causing system panic.
> Out of curiosity I am asking, how this change is useful here, is it reducing the re-connection
> time...Anyhow rpcrdma_clean_cq was discarding the completions (flush/successful both)
>

Well, I don't think there is anything restricting an application from destroying the QP with pending CQEs on its CQs. So it definitely shouldn't cause a BUG_ON() I think. I'll have to read up in the Verbs specs if destroying a QP kills all the pending CQEs...

> >
> >
> > >> -----Original Message-----
> > >> From: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org [mailto:linux-rdma-
> > >> owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org] On Behalf Of Chuck Lever
> > >> Sent: Tuesday, June 24, 2014 4:10 AM
> > >> To: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org; linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > >> Subject: [PATCH v1 05/13] xprtrdma: Don't drain CQs on transport
> > >> disconnect
> > >>
> > >> CQs are not destroyed until unmount. By draining CQs on transport
> > >> disconnect, successful completions that can change the r.frmr.state
> > >> field can be missed.
>
> Still those are missed isn’t it....Since those successful completions will still be dropped after re-
> connection. Am I missing something to
> understanding the motivation...
>
> > >>
> > >> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> > >> ---
> > >> net/sunrpc/xprtrdma/verbs.c | 5 -----
> > >> 1 file changed, 5 deletions(-)
> > >>
> > >> diff --git a/net/sunrpc/xprtrdma/verbs.c
> > >> b/net/sunrpc/xprtrdma/verbs.c index 3c7f904..451e100 100644
> > >> --- a/net/sunrpc/xprtrdma/verbs.c
> > >> +++ b/net/sunrpc/xprtrdma/verbs.c
> > >> @@ -873,9 +873,6 @@ retry:
> > >> dprintk("RPC: %s: rpcrdma_ep_disconnect"
> > >> " status %i\n", __func__, rc);
> > >>
> > >> - rpcrdma_clean_cq(ep->rep_attr.recv_cq);
> > >> - rpcrdma_clean_cq(ep->rep_attr.send_cq);
> > >> -
> > >> xprt = container_of(ia, struct rpcrdma_xprt, rx_ia);
> > >> id = rpcrdma_create_id(xprt, ia,
> > >> (struct sockaddr *)&xprt->rx_data.addr);
> > @@ -985,8 +982,6 @@
> > >> rpcrdma_ep_disconnect(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia)
> > >> {
> > >> int rc;
> > >>
> > >> - rpcrdma_clean_cq(ep->rep_attr.recv_cq);
> > >> - rpcrdma_clean_cq(ep->rep_attr.send_cq);
> > >> rc = rdma_disconnect(ia->ri_id);
> > >> if (!rc) {
> > >> /* returns without wait if not connected */
> > >>
> > >> --
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