Return-Path: Received: from aserp1050.oracle.com ([141.146.126.70]:30537 "EHLO aserp1050.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754065AbcHSCXn (ORCPT ); Thu, 18 Aug 2016 22:23:43 -0400 Received: from aserp1040.oracle.com (aserp1040.oracle.com [141.146.126.69]) by aserp1050.oracle.com (Sentrion-MTA-4.3.2/Sentrion-MTA-4.3.2) with ESMTP id u7IMC6S2022345 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Thu, 18 Aug 2016 22:12:06 GMT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: WARN_ON added to rpc_create() From: Chuck Lever In-Reply-To: <20160818215611.GA25052@fieldses.org> Date: Thu, 18 Aug 2016 18:11:43 -0400 Cc: "J. Bruce Fields" , Linux NFS Mailing List Message-Id: References: <42D0C152-58F9-4467-B86D-2A7A25544CE4@oracle.com> <20160803174724.GA5993@fieldses.org> <5E7D6A55-B7F3-411D-A74B-E8BCE04BCF02@oracle.com> <20160818215611.GA25052@fieldses.org> To: "J. Bruce Fields" Sender: linux-nfs-owner@vger.kernel.org List-ID: > On Aug 18, 2016, at 5:56 PM, J. Bruce Fields wrote: > > On Wed, Aug 03, 2016 at 03:40:11PM -0400, Chuck Lever wrote: >> >>> On Aug 3, 2016, at 1:47 PM, bfields@fieldses.org wrote: >>> >>> On Wed, Aug 03, 2016 at 11:27:47AM -0400, Chuck Lever wrote: >>>> Hi Bruce- >>>> >>>> I see that commit 39a9beab5acb83176e8b9a4f0778749a09341f1f >>>> Author: J. Bruce Fields >>>> AuthorDate: Tue May 17 12:38:21 2016 -0400 >>>> >>>> rpc: share one xps between all backchannels >>>> >>>> has added this piece of code: >>>> >>>> @@ -452,10 +452,20 @@ static struct rpc_clnt *rpc_create_xprt(struct rpc_create_args *args, >>>> struct rpc_clnt *clnt = NULL; >>>> struct rpc_xprt_switch *xps; >>>> >>>> - xps = xprt_switch_alloc(xprt, GFP_KERNEL); >>>> - if (xps == NULL) { >>>> - xprt_put(xprt); >>>> - return ERR_PTR(-ENOMEM); >>>> + if (args->bc_xprt && args->bc_xprt->xpt_bc_xps) { >>>> + WARN_ON(args->protocol != XPRT_TRANSPORT_BC_TCP); >>>> + xps = args->bc_xprt->xpt_bc_xps; >>>> + xprt_switch_get(xps); >>>> + } else { >>>> >>>> >>>> the WARN_ON here fires on the server whenever I use NFSv4.1 on RDMA. >>>> >>>> Can you say why it was added? Is there something RPC/RDMA needs to >>>> do to make the code safe? >>> >>> What is args->protocol in this case? >>> >>> Digging around... OK, I missed that BC_TCP and BC_RDMA were defined as >>> OR's of an XPRT_TRANSPORT_BC bit with the identifier of the underlying >>> transport. That makes sense. >>> >>> So, I should have just used XPRT_TRANSPORT_BC there--I think all I meant >>> was "is this a backchannel". >>> >>> Does that fix the problem? >> >> This simple fix eliminates the log noise: >> >> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c >> index 2808d55..f94caf7 100644 >> --- a/net/sunrpc/clnt.c >> +++ b/net/sunrpc/clnt.c >> @@ -520,7 +520,7 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args) >> char servername[48]; >> >> if (args->bc_xprt) { >> - WARN_ON(args->protocol != XPRT_TRANSPORT_BC_TCP); >> + WARN_ON(!(args->protocol & XPRT_TRANSPORT_BC)); >> xprt = args->bc_xprt->xpt_bc_xprt; >> if (xprt) { >> xprt_get(xprt); >> >> >> This code seems to come from: >> >> commit d50039ea5ee63c589b0434baa5ecf6e5075bb6f9 >> Author: J. Bruce Fields >> AuthorDate: Mon May 16 17:03:42 2016 -0400 >> >> nfsd4/rpc: move backchannel create logic into rpc code >> >> >> Where it may have been copied from: >> >> -static struct rpc_clnt *create_backchannel_client(struct rpc_create_args *args) >> -{ >> - struct rpc_xprt *xprt; >> - >> - if (args->protocol != XPRT_TRANSPORT_BC_TCP) >> - return rpc_create(args); >> - >> - xprt = args->bc_xprt->xpt_bc_xprt; >> - if (xprt) { >> - xprt_get(xprt); >> - return rpc_create_xprt(args, xprt); >> - } >> - >> - return rpc_create(args); >> -} >> >> There's no warning here. In fact, protocol != BC_TCP seems to >> be expected. > > The protocol should be BC_TCP (OK, actually just BC) if and only if > bc_xprt is set. > > (The BC_TCP case is the 4.1+ case, the other is the 4.0 case. In the > 4.1+ case, the new client uses an existing (client-initiated) > connection, in the 4.0 case, the new client must also have a new > connection. > > In the 4.0 case we'll always create a new xprt, in the 4.1 case we might > or might not--depends on whether that particular connection has been > used for a backchannel previously.) OK, but why is a WARN_ON needed here? Why not return -EINVAL, for example (once you've corrected BC_TCP -> BC) ? -- Chuck Lever