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 11CC725A659; Thu, 9 Oct 2025 12:22:35 +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=1760012556; cv=none; b=WPgIRm5rCmC5jyG2/nWx2O8dNPL43mh7PIh3Nx96O/a/hYUo+tK5L3jKvHO0d7ODVeq7UTQoSgnTvo0skLJ+v6VLpxvFI2t5dNCbRE/iQZtiwATf3BRO9K6GgvQqRZ7fDvsF4Ef5IMCFL1yOinmvBNZTT04IIKF5EMcz3r92XNM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760012556; c=relaxed/simple; bh=aah+6/bsNlVBqVpS6fQlXLjGlySjDM3Q1Kw6QKjebLM=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=sE39+Gi/3w8OY+zPb+SbC/yVsCmyj33YGJ+MWQaBbl8/FTalQ2xVmxWYgnJlkUL1JLXobIjU8PcFuGdYWsfjyXkHQz9Mx5H+kmeFAoTQAhV6+o4koa/vsz5cMp6x1THa7A2nwxQRf4WQoVku/i5YHDDSlfSa5ooy66mu/Qn9M5U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XHMYu9eH; 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="XHMYu9eH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C5E6C4CEE7; Thu, 9 Oct 2025 12:22:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760012555; bh=aah+6/bsNlVBqVpS6fQlXLjGlySjDM3Q1Kw6QKjebLM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=XHMYu9eHzbJETBVdjGe/S53qRUh7qx3hh2aguGeZzOp/MbKFccgGxMMXbxF5yeaHJ mAnX++LNeV4V//eQaAJqCo24TETt9Wwv1lbeuCyxpCjx9sMa0NB5VAVwYOFN4INGd4 BQCvhEV86hnYSe5TgtjMLCf+8iO5ksng3fbh1feKIkrOxcMsNC+ZqRkhu1AzecuTyo pfmsCJRiLtvwvtm6hFbSBzkxPjePNXKUXNwanIxSiUGfspK4NWa89F4o/qVhXVWzy0 dc5botkhgPTNTn8Kk8K24ataJioyJ5pIVKygieIh+qTjg1/xuuvasQ91B8jx6wQEds 5lSlUVFWFViuQ== Message-ID: <74e20200de3d113c0bced1380c0ce99a569c2892.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: Thu, 09 Oct 2025 08:22:33 -0400 In-Reply-To: <175996028564.1793333.11431539077389693375@noble.neil.brown.name> References: <20251008-rq_bvec-v2-0-823c0a85a27c@kernel.org> , <20251008-rq_bvec-v2-2-823c0a85a27c@kernel.org> <175996028564.1793333.11431539077389693375@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 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knfs= d > > 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 report= s > > attempting to send is short by 4 bytes): > >=20 > > rpc-srv/tcp: nfsd: sent 1048155 when sending 1048152 bytes - shutti= ng down socket > >=20 > > svc_tcp_sendmsg() steals a slot in the rq_bvec array for the TCP record > > marker. If the send is an unaligned READ call though, then there may no= t > > 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 the > > callers that care. > >=20 > > Fixes: e18e157bb5c8 ("SUNRPC: Send RPC message on TCP with a single soc= k_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 have > 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 uses > (and maybe you have already audited...). >=20 I get the objection. I'm not crazy about all of the adjustments either. 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. The RPC code mostly ignores the last slot in rq_pages array after it's allocated, but we need rq_bvec to treat it like any other slot, hence the adjustment here. I looked at just doing what you suggest first. It would fix it, but at the expense of keeping an extra page per nfsd thread. We could couple your suggested fix with just not allocating that last rq_pages slot, but we end up having to adjust more places than this change does. Also, at that point, rq_maxpages is not _really_ the max number of pages. Maybe what we need to do is move to a separate length field for rq_bvec? We have some existing holes in svc_rqst that could hold one and that would make the code more clear. I'll respin this and see how that looks. Thanks for the review! >=20 >=20 > >=20 > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > index 77f6879c2e063fa79865100bbc2d1e64eb332f42..c4e9300d657cf7fdba23f2f= 4e4bdaad9cd99d1a3 100644 > > --- a/fs/nfsd/vfs.c > > +++ b/fs/nfsd/vfs.c > > @@ -1111,7 +1111,7 @@ nfsd_direct_read(struct svc_rqst *rqstp, struct s= vc_fh *fhp, > > =20 > > v =3D 0; > > total =3D dio_end - dio_start; > > - while (total && v < rqstp->rq_maxpages && > > + while (total && v < rqstp->rq_maxpages + 1 && > > rqstp->rq_next_page < rqstp->rq_page_end) { > > len =3D min_t(size_t, total, PAGE_SIZE); > > bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page, > > @@ -1200,7 +1200,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, str= uct svc_fh *fhp, > > =20 > > v =3D 0; > > total =3D *count; > > - while (total && v < rqstp->rq_maxpages && > > + while (total && v < rqstp->rq_maxpages + 1 && > > rqstp->rq_next_page < rqstp->rq_page_end) { > > len =3D min_t(size_t, total, PAGE_SIZE - base); > > bvec_set_page(&rqstp->rq_bvec[v], *rqstp->rq_next_page, > > @@ -1318,7 +1318,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc= _fh *fhp, > > if (stable && !fhp->fh_use_wgather) > > kiocb.ki_flags |=3D IOCB_DSYNC; > > =20 > > - nvecs =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload= ); > > + nvecs =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages + 1, pay= load); > > iov_iter_bvec(&iter, ITER_SOURCE, rqstp->rq_bvec, nvecs, *cnt); > > since =3D READ_ONCE(file->f_wb_err); > > if (verf) > > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c > > index 4704dce7284eccc9e2bc64cf22947666facfa86a..919263a0c04e3f1afa60741= 4bc1893ba02206e38 100644 > > --- a/net/sunrpc/svc.c > > +++ b/net/sunrpc/svc.c > > @@ -706,7 +706,8 @@ svc_prepare_thread(struct svc_serv *serv, struct sv= c_pool *pool, int node) > > if (!svc_init_buffer(rqstp, serv, node)) > > goto out_enomem; > > =20 > > - rqstp->rq_bvec =3D kcalloc_node(rqstp->rq_maxpages, > > + /* +1 for the TCP record marker */ > > + rqstp->rq_bvec =3D kcalloc_node(rqstp->rq_maxpages + 1, > > sizeof(struct bio_vec), > > GFP_KERNEL, node); > > if (!rqstp->rq_bvec) > > diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c > > index 377fcaaaa061463fc5c85fc09c7a8eab5e06af77..5f8bb11b686bcd7302b9447= 6490ba9b1b9ddc06a 100644 > > --- a/net/sunrpc/svcsock.c > > +++ b/net/sunrpc/svcsock.c > > @@ -740,7 +740,7 @@ static int svc_udp_sendto(struct svc_rqst *rqstp) > > if (svc_xprt_is_dead(xprt)) > > goto out_notconn; > > =20 > > - count =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, xdr); > > + count =3D xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages + 1, xdr= ); > > =20 > > iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec, > > count, rqstp->rq_res.len); > > @@ -1244,7 +1244,7 @@ static int svc_tcp_sendmsg(struct svc_sock *svsk,= struct svc_rqst *rqstp, > > memcpy(buf, &marker, sizeof(marker)); > > bvec_set_virt(rqstp->rq_bvec, buf, sizeof(marker)); > > =20 > > - count =3D xdr_buf_to_bvec(rqstp->rq_bvec + 1, rqstp->rq_maxpages - 1, > > + count =3D xdr_buf_to_bvec(rqstp->rq_bvec + 1, rqstp->rq_maxpages, > > &rqstp->rq_res); > > =20 > > iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, rqstp->rq_bvec, > >=20 > > --=20 > > 2.51.0 > >=20 > >=20 --=20 Jeff Layton