From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 744812EDD6F; Fri, 10 Oct 2025 10:25:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760091919; cv=none; b=otFzdiCy9jsZsLk6SKC+fbRyf+NnFgVuqjuSHzttyICUq1JiVINTkw7/bNyYhsuwAI8YgoMeopik46KvMXYw0tjZKl2dD96dze30DuBD2pn999f66yl+D8FJZEsrSFXl/HCKWlJ+cT/41ITvPqrbvlxAXWTap6UCkdny9hM3JSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760091919; c=relaxed/simple; bh=MNkwg/xATN/ldK/6IBPyXEvWq0KrI+2Prr5kdlfm4ds=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=s5LETIQwxmvy21y+3PLCH0hBBQVFgn+Q6h5gPB04nMyBWF7OhXR/CXgaNFcbOT6HEbnKbTURz1Rvpt84v6psQvLBcnVmWZ1NxSLId3clNa5JI1tggWai31RZEoUBXqnzzv03IsoHpS6GRkb8NJsyxK4b1P63yMXA9ODAgJX/L2I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FQeFW2zZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FQeFW2zZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB2C9C4CEF1; Fri, 10 Oct 2025 10:25:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760091919; bh=MNkwg/xATN/ldK/6IBPyXEvWq0KrI+2Prr5kdlfm4ds=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=FQeFW2zZKWA4H8Y6oIBrY7cpWydjGZQcUZLu3Up/FA3TFdv3FkaWGWvxzZixX6XSj WtX7w+GjtGsE9NMGbgDFJoDSc7hpgGU3zCs1sgZRsTtTfvy2MTEnUTDWplXw5p1nSW ICpF3wLu8EwpRmRdbCJBa9EXbaxLlUy7psF53dyzEnaWC3k+9g9wD/y0MuylHdz9La 5cpOpl+FAb6OUyVb1I9dtsZMoMQThIinLjusW7MVtI+lAR0wjAbnmM/nnHaPc/6XJ2 eFFhvgQ+Fc3k0NBIR0oiyNlFqtLGPy7Jv5zZHvnK8GJHGlhMdZgKSZt0J15grbAo1H h5a2Nd8qXusCg== Message-ID: <8cbef9511c8b70dfcf7cdaa9a620f931ab170faa.camel@kernel.org> Subject: Re: [PATCH v2 2/2] sunrpc: add a slot to rqstp->rq_bvec for TCP record marker From: Jeff Layton To: NeilBrown Cc: Chuck Lever , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , David Howells , Brandon Adams , linux-nfs@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 10 Oct 2025 06:25:16 -0400 In-Reply-To: <176005502018.1793333.5043420085151021396@noble.neil.brown.name> References: <>, <74e20200de3d113c0bced1380c0ce99a569c2892.camel@kernel.org> <176005502018.1793333.5043420085151021396@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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like this in dmesg on some = knfsd > > > > servers: > > > >=20 > > > > xdr_buf_to_bvec: bio_vec array overflow > > > >=20 > > > > Usually followed by messages like this that indicate a short send (= note > > > > that this message is from an older kernel and the amount that it re= ports > > > > attempting to send is short by 4 bytes): > > > >=20 > > > > rpc-srv/tcp: nfsd: sent 1048155 when sending 1048152 bytes - sh= utting down socket > > > >=20 > > > > svc_tcp_sendmsg() steals a slot in the rq_bvec array for the TCP re= cord > > > > marker. If the send is an unaligned READ call though, then there ma= y not > > > > be enough slots in the rq_bvec array in some cases. > > > >=20 > > > > Add a slot to the rq_bvec array, and fix up the array lengths in th= e > > > > callers that care. > > > >=20 > > > > Fixes: e18e157bb5c8 ("SUNRPC: Send RPC message on TCP with a single= sock_sendmsg() call") > > > > Tested-by: Brandon Adams > > > > Signed-off-by: Jeff Layton > > > > --- > > > > fs/nfsd/vfs.c | 6 +++--- > > > > net/sunrpc/svc.c | 3 ++- > > > > net/sunrpc/svcsock.c | 4 ++-- > > > > 3 files changed, 7 insertions(+), 6 deletions(-) > > >=20 > > > I can't say that I'm liking this patch. > > >=20 > > > There are 11 place where (in nfsd-testing recently) where > > > rq_maxpages is used (as opposed to declared or assigned). > > >=20 > > > 3 in nfsd/vfs.c > > > 4 in sunrpc/svc.c > > > 1 in sunrpc/svc_xprt.c > > > 2 in sunrpc/svcsock.c > > > 1 in xprtrdma/svc_rdma_rc.c > > >=20 > > > Your patch changes six of those to add 1. I guess the others aren't > > > "callers that care". It would help to have it clearly stated why, or > > > why not, a caller might care. > > >=20 > > > But also, what does "rq_maxpages" even mean now? > > > The comment in svc.h still says "num of entries in rq_pages" > > > which is certainly no longer the case. > > > But if it was the case, we should have called it "rq_numpages" > > > or similar. > > > But maybe it wasn't meant to be the number of pages in the array, > > > maybe it was meant to be the maximum number of pages is a request > > > or a reply..... > > > No - that is sv_max_mesg, to which we add 2 and 1. > > > So I could ask "why not just add another 1 in svc_serv_maxpages()?" > > > Would the callers that might not care be harmed if rq_maxpages were > > > one larger than it is? > > >=20 > > > It seems to me that rq_maxpages is rather confused and the bug you ha= ve > > > found which requires this patch is some evidence to that confusion. = We > > > should fix the confusion, not just the bug. > > >=20 > > > So simple question to cut through my waffle: > > > Would this: > > > - return DIV_ROUND_UP(serv->sv_max_mesg, PAGE_SIZE) + 2 + 1; > > > + return DIV_ROUND_UP(serv->sv_max_mesg, PAGE_SIZE) + 2 + 1 + 1; > > >=20 > > > fix the problem. If not, why not? If so, can we just do this? > > > then look at renaming rq_maxpages to rq_numpages and audit all the us= es > > > (and maybe you have already audited...). > > >=20 > >=20 > > I get the objection. I'm not crazy about all of the adjustments either. > >=20 > > rq_maxpages is used to size two fields in the rqstp: rq_pages and > > rq_bvec. It turns out that they both want rq_maxpages + 1 slots. The > > rq_pages array needs the extra slot for a NULL terminator, and rq_bvec > > needs it for the TCP record marker. >=20 > Somehow the above para helped a lot for me to understand what the issue > is here - thanks. >=20 > rq_bvec is used for two quite separate purposes. >=20 > nfsd/vfs.c uses it to assemble read/write requests to send to the > filesystem. > sunrpc/svcsock.c uses to assemble send/recv requests to send to the > network. >=20 > It might help me if this were documented clearly in svc.h as I seem to > have had to discover several times now :-( >=20 > Should these even use the same rq_bvec? I guess it makes sense to share > but we should be cautious about letting the needs of one side infect the > code of the other side. >=20 > So if we increase the size of rq_bvec to meet the needs of svcsock.c, do > we need to make *any* code changes to vfs.c? I doubt it. >=20 > It bothers me a little bit that svc_tcp_sendmsg() needs to allocate a > frag. But given that it does, could it also allocate a larger bvec if > rq_bvec isn't big enough? >=20 > Or should svc_tcp_recvfrom() allocate the frag and make sure the bvec is > big enough ...... > Or svc_alloc_arg() could check with each active transport for any > preallocation requirements... > Or svc_create_socket() could update some "bvec_size" field in svc_serv > which svc_alloc_arg() could check an possibly realloc rq_bvec. >=20 > I'm rambling a bit here. I agree with Chuck (and you) that it would be > nice if this need for a larger bvec were kept local to svcsock code if > possible. >=20 > But I'm fairly confident that the current problem doesn't justify any > changes to vfs.c. svc.c probably needs to somehow be involved in > rq_bvec being bigger and svcsock.c certainly needs to be able to make > use of the extra space, but that seems to be all that is required. >=20 I sent a v3 patch which adds a separate rq_bvec_len field and uses that in the places where the code is iterating over the rq_bvec. That does change places in vfs.c, but I think it makes the code clearer. Are you OK with that version? Thanks, --=20 Jeff Layton