From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 4E8213793BF; Fri, 29 May 2026 17:06:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780074384; cv=none; b=rlts6PQbpNCw6qoAWk3D36/ZfUeezcwtlOgvWu7aKCeT6CP6HhZXXRRC7NIcllFVKXCuVs5hRZGqfMYFubWlwcBLUKjiMu7WgESFGRTzLpG7XmbR6s3BuoSxE4b3P/SPRLb1YUcJLWSdhT6Gh4WQItZctyMek8cF1opwX2KH/Wk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780074384; c=relaxed/simple; bh=rZ8cPi2EM2ZZ4Sw8c4ruDBEIDFBEvDjGCrzw9KjdyuY=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=H3WmjXdd0aMr6YwATZ5cM6YY6ferH27gHRtDrA2O0rFv5E7Aeb6V5FeuWCSoHUI+9RXvGaQ+4EoQozn3K7htSNvhMkkU6QW1uVpvKV0ly3EXQX0mBEhJfyhekhaoj+Y35iX3lf/qqEXiiK81JITAALzpl5RUi3PLAG33QF+L6Do= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jhazZLKy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jhazZLKy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A67521F00893; Fri, 29 May 2026 17:06:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780074383; bh=25LXI7pSTxSGPDme0K0zF5dohmDJt5M4raZtuqmVpQk=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=jhazZLKy8Ak6nqc8pdK8FR74WsrGcDMX/evWqDFDVQGcdyrQwAN/232RIpNBtJFgx L8jdAbi1giPU5z9OGV79PoiVBpMWGRy86K1p/zwHdu5fumlG5Vroo1Cwo1AbOYtNNp r1bYBoHF27RgN1lK3GJYjP3UJV+P+Q79rpfeG1TEabrXdOnS/Q53r93vQQ2VEBzvGj 7JUKJCdBJHBMAkZnqzj8ZdaIOmpX4iWBVTD1gGxEKI38rYx7EogehFDGRQopcNXtrC NfmGgsgDIwT12Na4P7Vd85G0S4bAE12lVon4g7STO7JF5FiL/pGzdNRRsdPpk9N/nO 53UFi9vaYlOBw== Message-ID: Subject: Re: [PATCH 08/10] nfsd: fix partial-write detection in nfsd_direct_write From: Jeff Layton To: Chuck Lever , Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , "J. Bruce Fields" , Scott Mayhew , Trond Myklebust , Andreas Gruenbacher , Mike Snitzer , Rick Macklem Cc: Chris Mason , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 29 May 2026 13:06:19 -0400 In-Reply-To: <0f23fe53-3796-4102-ab62-f28fd53afaf7@kernel.org> References: <20260528-nfsd-fixes-v1-0-e78708eff77d@kernel.org> <20260528-nfsd-fixes-v1-8-e78708eff77d@kernel.org> <5ef47df4-c9f4-4b7a-a493-71be1a95ee90@app.fastmail.com> <1ab23163ff7e1b7f01326ef9f222dad25ad6a863.camel@kernel.org> <0f23fe53-3796-4102-ab62-f28fd53afaf7@kernel.org> 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 VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf CBYyUE8QJpvTZyfUHNYldXlrjO6n5MdOempLqWpfOmcGkwnyNRBR46g/jf8KnPRwXs509yAqDB6sE LZH+yWr9LQZEwARAQABtCVKZWZmIExheXRvbiA8amxheXRvbkBwb29jaGllcmVkcy5uZXQ+iQI7BB MBAgAlAhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAUCTpXWPAIZAQAKCRAADmhBGVaCFc65D/4 gBLNMHopQYgG/9RIM3kgFCCQV0pLv0hcg1cjr+bPI5f1PzJoOVi9s0wBDHwp8+vtHgYhM54yt43uI 7Htij0RHFL5eFqoVT4TSfAg2qlvNemJEOY0e4daljjmZM7UtmpGs9NN0r9r50W82eb5Kw5bc/r0km R/arUS2st+ecRsCnwAOj6HiURwIgfDMHGPtSkoPpu3DDp/cjcYUg3HaOJuTjtGHFH963B+f+hyQ2B rQZBBE76ErgTDJ2Db9Ey0kw7VEZ4I2nnVUY9B5dE2pJFVO5HJBMp30fUGKvwaKqYCU2iAKxdmJXRI ONb7dSde8LqZahuunPDMZyMA5+mkQl7kpIpR6kVDIiqmxzRuPeiMP7O2FCUlS2DnJnRVrHmCljLkZ Wf7ZUA22wJpepBligemtSRSbqCyZ3B48zJ8g5B8xLEntPo/NknSJaYRvfEQqGxgk5kkNWMIMDkfQO lDSXZvoxqU9wFH/9jTv1/6p8dHeGM0BsbBLMqQaqnWiVt5mG92E1zkOW69LnoozE6Le+12DsNW7Rj iR5K+27MObjXEYIW7FIvNN/TQ6U1EOsdxwB8o//Yfc3p2QqPr5uS93SDDan5ehH59BnHpguTc27Xi QQZ9EGiieCUx6Zh2ze3X2UW9YNzE15uKwkkuEIj60NvQRmEDfweYfOfPVOueC+iFifbQgSmVmZiBM YXl0b24gPGpsYXl0b25AcmVkaGF0LmNvbT6JAjgEEwECACIFAk6V0q0CGwMGCwkIBwMCBhUIAgkKC wQWAgMBAh4BAheAAAoJEAAOaEEZVoIViKUQALpvsacTMWWOd7SlPFzIYy2/fjvKlfB/Xs4YdNcf9q LqF+lk2RBUHdR/dGwZpvw/OLmnZ8TryDo2zXVJNWEEUFNc7wQpl3i78r6UU/GUY/RQmOgPhs3epQC 3PMJj4xFx+VuVcf/MXgDDdBUHaCTT793hyBeDbQuciARDJAW24Q1RCmjcwWIV/pgrlFa4lAXsmhoa c8UPc82Ijrs6ivlTweFf16VBc4nSLX5FB3ls7S5noRhm5/Zsd4PGPgIHgCZcPgkAnU1S/A/rSqf3F LpU+CbVBDvlVAnOq9gfNF+QiTlOHdZVIe4gEYAU3CUjbleywQqV02BKxPVM0C5/oVjMVx3bri75n1 TkBYGmqAXy9usCkHIsG5CBHmphv9MHmqMZQVsxvCzfnI5IO1+7MoloeeW/lxuyd0pU88dZsV/riHw 87i2GJUJtVlMl5IGBNFpqoNUoqmvRfEMeXhy/kUX4Xc03I1coZIgmwLmCSXwx9MaCPFzV/dOOrju2 xjO+2sYyB5BNtxRqUEyXglpujFZqJxxau7E0eXoYgoY9gtFGsspzFkVNntamVXEWVVgzJJr/EWW0y +jNd54MfPRqH+eCGuqlnNLktSAVz1MvVRY1dxUltSlDZT7P2bUoMorIPu8p7ZCg9dyX1+9T6Muc5d Hxf/BBP/ir+3e8JTFQBFOiLNdFtB9KZWZmIExheXRvbiA8amxheXRvbkBzYW1iYS5vcmc+iQI4BBM BAgAiBQJOldK9AhsDBgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRAADmhBGVaCFWgWD/0ZRi4h N9FK2BdQs9RwNnFZUr7JidAWfCrs37XrA/56olQl3ojn0fQtrP4DbTmCuh0SfMijB24psy1GnkPep naQ6VRf7Dxg/Y8muZELSOtsv2CKt3/02J1BBitrkkqmHyni5fLLYYg6fub0T/8Kwo1qGPdu1hx2BQ RERYtQ/S5d/T0cACdlzi6w8rs5f09hU9Tu4qV1JLKmBTgUWKN969HPRkxiojLQziHVyM/weR5Reu6 FZVNuVBGqBD+sfk/c98VJHjsQhYJijcsmgMb1NohAzwrBKcSGKOWJToGEO/1RkIN8tqGnYNp2G+aR 685D0chgTl1WzPRM6mFG1+n2b2RR95DxumKVpwBwdLPoCkI24JkeDJ7lXSe3uFWISstFGt0HL8Eew P8RuGC8s5h7Ct91HMNQTbjgA+Vi1foWUVXpEintAKgoywaIDlJfTZIl6Ew8ETN/7DLy8bXYgq0Xzh aKg3CnOUuGQV5/nl4OAX/3jocT5Cz/OtAiNYj5mLPeL5z2ZszjoCAH6caqsF2oLyAnLqRgDgR+wTQ T6gMhr2IRsl+cp8gPHBwQ4uZMb+X00c/Amm9VfviT+BI7B66cnC7Zv6Gvmtu2rEjWDGWPqUgccB7h dMKnKDthkA227/82tYoFiFMb/NwtgGrn5n2vwJyKN6SEoygGrNt0SI84y6hEVbQlSmVmZiBMYXl0b 24gPGpsYXl0b25AcHJpbWFyeWRhdGEuY29tPokCOQQTAQIAIwUCU4xmKQIbAwcLCQgHAwIBBhUIAg kKCwQWAgMBAh4BAheAAAoJEAAOaEEZVoIV1H0P/j4OUTwFd7BBbpoSp695qb6HqCzWMuExsp8nZjr uymMaeZbGr3OWMNEXRI1FWNHMtcMHWLP/RaDqCJil28proO+PQ/yPhsr2QqJcW4nr91tBrv/MqItu AXLYlsgXqp4BxLP67bzRJ1Bd2x0bWXurpEXY//VBOLnODqThGEcL7jouwjmnRh9FTKZfBDpFRaEfD FOXIfAkMKBa/c9TQwRpx2DPsl3eFWVCNuNGKeGsirLqCxUg5kWTxEorROppz9oU4HPicL6rRH22Ce 6nOAON2vHvhkUuO3GbffhrcsPD4DaYup4ic+DxWm+DaSSRJ+e1yJvwi6NmQ9P9UAuLG93S2MdNNbo sZ9P8k2mTOVKMc+GooI9Ve/vH8unwitwo7ORMVXhJeU6Q0X7zf3SjwDq2lBhn1DSuTsn2DbsNTiDv qrAaCvbsTsw+SZRwF85eG67eAwouYk+dnKmp1q57LDKMyzysij2oDKbcBlwB/TeX16p8+LxECv51a sjS9TInnipssssUDrHIvoTTXWcz7Y5wIngxDFwT8rPY3EggzLGfK5Zx2Q5S/N0FfmADmKknG/D8qG IcJE574D956tiUDKN4I+/g125ORR1v7bP+OIaayAvq17RP+qcAqkxc0x8iCYVCYDouDyNvWPGRhbL UO7mlBpjW9jK9e2fvZY9iw3QzIPGKtClKZWZmIExheXRvbiA8amVmZi5sYXl0b25AcHJpbWFyeWRh dGEuY29tPokCOQQTAQIAIwUCU4xmUAIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEAAOa EEZVoIVzJoQALFCS6n/FHQS+hIzHIb56JbokhK0AFqoLVzLKzrnaeXhE5isWcVg0eoV2oTScIwUSU apy94if69tnUo4Q7YNt8/6yFM6hwZAxFjOXR0ciGE3Q+Z1zi49Ox51yjGMQGxlakV9ep4sV/d5a50 M+LFTmYSAFp6HY23JN9PkjVJC4PUv5DYRbOZ6Y1+TfXKBAewMVqtwT1Y+LPlfmI8dbbbuUX/kKZ5d dhV2736fgyfpslvJKYl0YifUOVy4D1G/oSycyHkJG78OvX4JKcf2kKzVvg7/Rnv+AueCfFQ6nGwPn 0P91I7TEOC4XfZ6a1K3uTp4fPPs1Wn75X7K8lzJP/p8lme40uqwAyBjk+IA5VGd+CVRiyJTpGZwA0 jwSYLyXboX+Dqm9pSYzmC9+/AE7lIgpWj+3iNisp1SWtHc4pdtQ5EU2SEz8yKvDbD0lNDbv4ljI7e flPsvN6vOrxz24mCliEco5DwhpaaSnzWnbAPXhQDWb/lUgs/JNk8dtwmvWnqCwRqElMLVisAbJmC0 BhZ/Ab4sph3EaiZfdXKhiQqSGdK4La3OTJOJYZphPdGgnkvDV9Pl1QZ0ijXQrVIy3zd6VCNaKYq7B AKidn5g/2Q8oio9Tf4XfdZ9dtwcB+bwDJFgvvDYaZ5bI3ln4V3EyW5i2NfXazz/GA/I/ZtbsigCFc 8ftCBKZWZmIExheXRvbiA8amxheXRvbkBrZXJuZWwub3JnPokCOAQTAQIAIgUCWe8u6AIbAwYLCQg HAwIGFQgCCQoLBBYCAwECHgECF4AACgkQAA5oQRlWghUuCg/+Lb/xGxZD2Q1oJVAE37uW308UpVSD 2tAMJUvFTdDbfe3zKlPDTuVsyNsALBGclPLagJ5ZTP+Vp2irAN9uwBuacBOTtmOdz4ZN2tdvNgozz uxp4CHBDVzAslUi2idy+xpsp47DWPxYFIRP3M8QG/aNW052LaPc0cedYxp8+9eiVUNpxF4SiU4i9J DfX/sn9XcfoVZIxMpCRE750zvJvcCUz9HojsrMQ1NFc7MFT1z3MOW2/RlzPcog7xvR5ENPH19ojRD CHqumUHRry+RF0lH00clzX/W8OrQJZtoBPXv9ahka/Vp7kEulcBJr1cH5Wz/WprhsIM7U9pse1f1g Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (3.60.1-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2026-05-29 at 13:03 -0400, Chuck Lever wrote: > On 5/29/26 1:01 PM, Jeff Layton wrote: > > On Fri, 2026-05-29 at 12:57 -0400, Chuck Lever wrote: > > >=20 > > > On Thu, May 28, 2026, at 5:55 PM, Jeff Layton wrote: > > > > From: Chris Mason > > > >=20 > > > > nfsd_direct_write() walks a list of write segments and, after each > > > > vfs_iocb_iter_write(), tries to detect a short write so the loop ca= n > > > > stop before placing the next segment at a wrong file offset: > > > >=20 > > > > host_err =3D vfs_iocb_iter_write(file, kiocb, &segments[i].iter= ); > > > > if (host_err < 0) > > > > return host_err; > > > > *cnt +=3D host_err; > > > > if (host_err < segments[i].iter.count) > > > > break; /* partial write */ > > > >=20 > > > > vfs_iocb_iter_write() runs the iter through ->write_iter(), which > > > > advances the iter by the number of bytes written. By the time the > > > > check runs, segments[i].iter.count is the residual, not the origina= l > > > > request length: > > > >=20 > > > > before write_iter: iter.count =3D=3D original_len > > > > after write_iter: iter.count =3D=3D original_len - host_err > > > >=20 > > > > The condition then reduces to host_err < original_len - host_err, s= o > > > > the break fires only when less than half of the segment was written= . > > > > Any short write completing between 50% and 99% of the segment slips > > > > through; the loop advances to the next segment with kiocb->ki_pos > > > > only bumped by the short amount, writing the next segment's payload > > > > at the wrong offset and over-reporting *cnt to the NFS client. > > > >=20 > > > > Snapshot the segment's byte count before the write and compare > > > > host_err against that snapshot so any short write breaks the loop. > > > >=20 > > > > Fixes: 06c5c97293e3 ("NFSD: Implement NFSD_IO_DIRECT for NFS WRITE"= ) > > > > Assisted-by: kres:claude-opus-4-7 > > > > Signed-off-by: Chris Mason > > > > --- > > > > fs/nfsd/vfs.c | 5 ++++- > > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > >=20 > > > > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c > > > > index 980217f755b7..619f252af4d1 100644 > > > > --- a/fs/nfsd/vfs.c > > > > +++ b/fs/nfsd/vfs.c > > > > @@ -1380,6 +1380,7 @@ nfsd_direct_write(struct svc_rqst *rqstp, str= uct=20 > > > > svc_fh *fhp, > > > > struct file *file =3D nf->nf_file; > > > > unsigned int nsegs, i; > > > > ssize_t host_err; > > > > + size_t expected; > > > >=20 > > > > nsegs =3D nfsd_write_dio_iters_init(nf, rqstp->rq_bvec, nvecs, > > > > kiocb, *cnt, segments); > > > > @@ -1401,11 +1402,13 @@ nfsd_direct_write(struct svc_rqst *rqstp,= =20 > > > > struct svc_fh *fhp, > > > > kiocb->ki_flags |=3D IOCB_DONTCACHE; > > > > } > > > >=20 > > > > + expected =3D iov_iter_count(&segments[i].iter); > > > > + > > > > host_err =3D vfs_iocb_iter_write(file, kiocb, &segments[i].iter)= ; > > > > if (host_err < 0) > > > > return host_err; > > > > *cnt +=3D host_err; > > > > - if (host_err < segments[i].iter.count) > > > > + if (host_err < (ssize_t)expected) > > > > break; /* partial write */ > > > > } > > > >=20 > > > >=20 > > > > --=20 > > > > 2.54.0 > > >=20 > > > How many filesystems can return a short write in this case? > > > My impression was that only the NFS client can do that. > > >=20 > >=20 > > No idea right offhand, but NFS is exportable. Since > > vfs_iocb_iter_write() is allowed to return a short write, I think we > > have to deal with that properly here. >=20 > NFSD_IO_DIRECT is experimental, and doesn't make sense (to me) > to use with an NFS re-export. >=20 > If we can find another filesystem that might return a short write > with NFSD_IO_DIRECT, I might consider this a higher priority. >=20 I'm fairly sure Ceph and CIFS can and they're exportable. For local filesystems, I'm not even sure how to audit that. Given that the potential effect is data corruption, omitting this patch based on guesswork about what filesystems are being exported seems unwise. --=20 Jeff Layton