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 A05BF18BB86; Tue, 3 Sep 2024 15:19:47 +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=1725376787; cv=none; b=PTzWFb54mBaT8kNvFPhY62DaQWapfRCowwbSpofUdFTOBoWf1vuHncSZiMu6yhOjuHDLakZuV9NepzLf/iaE3xcYFQiGeZD/NxzHPYuzwlYx+l160KLv6mkmMjzMV6YfNfI84/7oYesGF8KEXrW2f0QUgs3bIEi5jW+TS12FtMg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725376787; c=relaxed/simple; bh=hMPpbLQB0V0EE1CVeU6Nxs6EZl9JUpoxTEj3Y7ZltTQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=g7UijTp4qeZnsF5e8uYVNAEcki6nt6Qy/MrRgJedS/LklFU9IuOjqwYrFtMTuKYxNoayABRBXg+PdDKSrPKXIdaGYOGpyKeaWLAViNVGuHYXlESRDkgyUUTX8UZCc0xY4vIh0LIoT/4dKSfy28y3amIE1hSVaCWrRM5+KyidIh8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bIXBV+62; 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="bIXBV+62" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8FBD9C4CEC8; Tue, 3 Sep 2024 15:19:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725376787; bh=hMPpbLQB0V0EE1CVeU6Nxs6EZl9JUpoxTEj3Y7ZltTQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=bIXBV+62Jx8VgnR9/SiOtvTx4tyiVxa/MmPwWkPFve/G/zhb0kGlQ37d8bDDCBtVR 1x3B0k3g4jp0Us7Vq46hk0b9dWq8b1IooO885IsD/PuVaBGlRnqr8rqIbNGTFkxfH9 DSVCFwk3Baj5zV1L66Xzx9XMggnNh9UQArmOvTL//FI/Osv1Uwp+Gu5JBTp8lZNM1X MQCAimBK7B3YGaHEfxg7VpxURxc9j743eWFyiqlYLD2rLAFMJIFKxAT26gnSkZah9p l/9VIKOe3n5NbB7YCNzgq05Q7fOG3PtI6426SS2FyBAaXQJ3kWaUupVOoociQmQTxW NARrd+OQ31+Zw== Message-ID: <981320f318d23fe02ed7597a56d13227f7cea31e.camel@kernel.org> Subject: Re: [PATCH v15 16/26] nfsd: add LOCALIO support From: Jeff Layton To: Mike Snitzer Cc: Chuck Lever , linux-nfs@vger.kernel.org, Anna Schumaker , Trond Myklebust , NeilBrown , linux-fsdevel@vger.kernel.org Date: Tue, 03 Sep 2024 11:19:45 -0400 In-Reply-To: References: <20240831223755.8569-1-snitzer@kernel.org> <20240831223755.8569-17-snitzer@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 3.52.4 (3.52.4-1.fc40) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2024-09-03 at 11:00 -0400, Mike Snitzer wrote: > On Tue, Sep 03, 2024 at 10:40:28AM -0400, Jeff Layton wrote: > > On Tue, 2024-09-03 at 10:34 -0400, Chuck Lever wrote: > > > On Sat, Aug 31, 2024 at 06:37:36PM -0400, Mike Snitzer wrote: > > > > From: Weston Andros Adamson > > > >=20 > > > > Add server support for bypassing NFS for localhost reads, writes, a= nd > > > > commits. This is only useful when both the client and server are > > > > running on the same host. > > > >=20 > > > > If nfsd_open_local_fh() fails then the NFS client will both retry a= nd > > > > fallback to normal network-based read, write and commit operations = if > > > > localio is no longer supported. > > > >=20 > > > > Care is taken to ensure the same NFS security mechanisms are used > > > > (authentication, etc) regardless of whether localio or regular NFS > > > > access is used. The auth_domain established as part of the traditi= onal > > > > NFS client access to the NFS server is also used for localio. Stor= e > > > > auth_domain for localio in nfsd_uuid_t and transfer it to the clien= t > > > > if it is local to the server. > > > >=20 > > > > Relative to containers, localio gives the client access to the netw= ork > > > > namespace the server has. This is required to allow the client to > > > > access the server's per-namespace nfsd_net struct. > > > >=20 > > > > This commit also introduces the use of NFSD's percpu_ref to interlo= ck > > > > nfsd_destroy_serv and nfsd_open_local_fh, to ensure nn->nfsd_serv i= s > > > > not destroyed while in use by nfsd_open_local_fh and other LOCALIO > > > > client code. > > > >=20 > > > > CONFIG_NFS_LOCALIO enables NFS server support for LOCALIO. > > > >=20 > > > > Signed-off-by: Weston Andros Adamson > > > > Signed-off-by: Trond Myklebust > > > > Co-developed-by: Mike Snitzer > > > > Signed-off-by: Mike Snitzer > > > > Co-developed-by: NeilBrown > > > > Signed-off-by: NeilBrown > > > >=20 > > > > Not-Acked-by: Chuck Lever > > > > Not-Reviewed-by: Jeff Layton > > > > --- > > > > fs/nfsd/Makefile | 1 + > > > > fs/nfsd/filecache.c | 2 +- > > > > fs/nfsd/localio.c | 112 +++++++++++++++++++++++++++++++++= ++++ > > > > fs/nfsd/netns.h | 4 ++ > > > > fs/nfsd/nfsctl.c | 25 ++++++++- > > > > fs/nfsd/trace.h | 3 +- > > > > fs/nfsd/vfs.h | 2 + > > > > include/linux/nfslocalio.h | 8 +++ > > > > 8 files changed, 154 insertions(+), 3 deletions(-) > > > > create mode 100644 fs/nfsd/localio.c > > > >=20 > > > > diff --git a/fs/nfsd/Makefile b/fs/nfsd/Makefile > > > > index b8736a82e57c..18cbd3fa7691 100644 > > > > --- a/fs/nfsd/Makefile > > > > +++ b/fs/nfsd/Makefile > > > > @@ -23,3 +23,4 @@ nfsd-$(CONFIG_NFSD_PNFS) +=3D nfs4layouts.o > > > > nfsd-$(CONFIG_NFSD_BLOCKLAYOUT) +=3D blocklayout.o blocklayoutxdr.= o > > > > nfsd-$(CONFIG_NFSD_SCSILAYOUT) +=3D blocklayout.o blocklayoutxdr.o > > > > nfsd-$(CONFIG_NFSD_FLEXFILELAYOUT) +=3D flexfilelayout.o flexfilel= ayoutxdr.o > > > > +nfsd-$(CONFIG_NFS_LOCALIO) +=3D localio.o > > > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > > > index 89ff380ec31e..348c1b97092e 100644 > > > > --- a/fs/nfsd/filecache.c > > > > +++ b/fs/nfsd/filecache.c > > > > @@ -52,7 +52,7 @@ > > > > #define NFSD_FILE_CACHE_UP (0) > > > > =20 > > > > /* We only care about NFSD_MAY_READ/WRITE for this cache */ > > > > -#define NFSD_FILE_MAY_MASK (NFSD_MAY_READ|NFSD_MAY_WRITE) > > > > +#define NFSD_FILE_MAY_MASK (NFSD_MAY_READ|NFSD_MAY_WRITE|NFSD_MAY_= LOCALIO) > > > > =20 > > > > static DEFINE_PER_CPU(unsigned long, nfsd_file_cache_hits); > > > > static DEFINE_PER_CPU(unsigned long, nfsd_file_acquisitions); > > > > diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c > > > > new file mode 100644 > > > > index 000000000000..75df709c6903 > > > > --- /dev/null > > > > +++ b/fs/nfsd/localio.c > > > > @@ -0,0 +1,112 @@ > > > > +// SPDX-License-Identifier: GPL-2.0-only > > > > +/* > > > > + * NFS server support for local clients to bypass network stack > > > > + * > > > > + * Copyright (C) 2014 Weston Andros Adamson > > > > + * Copyright (C) 2019 Trond Myklebust > > > > + * Copyright (C) 2024 Mike Snitzer > > > > + * Copyright (C) 2024 NeilBrown > > > > + */ > > > > + > > > > +#include > > > > +#include > > > > +#include > > > > +#include > > > > +#include > > > > +#include > > > > +#include > > > > + > > > > +#include "nfsd.h" > > > > +#include "vfs.h" > > > > +#include "netns.h" > > > > +#include "filecache.h" > > > > + > > > > +static const struct nfsd_localio_operations nfsd_localio_ops =3D { > > > > + .nfsd_open_local_fh =3D nfsd_open_local_fh, > > > > + .nfsd_file_put_local =3D nfsd_file_put_local, > > > > + .nfsd_file_file =3D nfsd_file_file, > > > > +}; > > > > + > > > > +void nfsd_localio_ops_init(void) > > > > +{ > > > > + memcpy(&nfs_to, &nfsd_localio_ops, sizeof(nfsd_localio_ops)); > > > > +} > > >=20 > > > Same comment as Neil: this should surface a pointer to the > > > localio_ops struct. Copying the whole set of function pointers is > > > generally unnecessary. > > >=20 > > >=20 > > > > + > > > > +/** > > > > + * nfsd_open_local_fh - lookup a local filehandle @nfs_fh and map = to nfsd_file > > > > + * > > > > + * @uuid: nfs_uuid_t which provides the 'struct net' to get the pr= oper nfsd_net > > > > + * and the 'struct auth_domain' required for LOCALIO access > > > > + * @rpc_clnt: rpc_clnt that the client established, used for socka= ddr and cred > > > > + * @cred: cred that the client established > > > > + * @nfs_fh: filehandle to lookup > > > > + * @fmode: fmode_t to use for open > > > > + * > > > > + * This function maps a local fh to a path on a local filesystem. > > > > + * This is useful when the nfs client has the local server mounted= - it can > > > > + * avoid all the NFS overhead with reads, writes and commits. > > > > + * > > > > + * On successful return, returned nfsd_file will have its nf_net m= ember > > > > + * set. Caller (NFS client) is responsible for calling nfsd_serv_p= ut and > > > > + * nfsd_file_put (via nfs_to.nfsd_file_put_local). > > > > + */ > > > > +struct nfsd_file * > > > > +nfsd_open_local_fh(nfs_uuid_t *uuid, > > > > + struct rpc_clnt *rpc_clnt, const struct cred *cred, > > > > + const struct nfs_fh *nfs_fh, const fmode_t fmode) > > > > + __must_hold(rcu) > > > > +{ > > > > + int mayflags =3D NFSD_MAY_LOCALIO; > > > > + struct nfsd_net *nn =3D NULL; > > > > + struct net *net; > > > > + struct svc_cred rq_cred; > > > > + struct svc_fh fh; > > > > + struct nfsd_file *localio; > > > > + __be32 beres; > > > > + > > > > + if (nfs_fh->size > NFS4_FHSIZE) > > > > + return ERR_PTR(-EINVAL); > > > > + > > > > + /* > > > > + * Not running in nfsd context, so must safely get reference on n= fsd_serv. > > > > + * But the server may already be shutting down, if so disallow ne= w localio. > > > > + * uuid->net is NOT a counted reference, but caller's rcu_read_lo= ck() ensures > > > > + * that if uuid->net is not NULL, then calling nfsd_serv_try_get(= ) is safe > > > > + * and if it succeeds we will have an implied reference to the ne= t. > > > > + */ > > > > + net =3D rcu_dereference(uuid->net); > > > > + if (net) > > > > + nn =3D net_generic(net, nfsd_net_id); > > > > + if (unlikely(!nn || !nfsd_serv_try_get(nn))) > > > > + return ERR_PTR(-ENXIO); > > > > + > > > > + /* Drop the rcu lock for nfsd_file_acquire_local() */ > > > > + rcu_read_unlock(); > > >=20 > > > I'm struggling with the locking logistics. Caller takes the RCU read > > > lock, this function drops the lock, then takes it again. So: > > >=20 > > > - A caller might rely on the lock being held continuously, but > > > - The API contract documented above doesn't indicate that this > > > function drops that lock > > > - The __must_hold(rcu) annotation doesn't indicate that this > > > function drops that lock, IIUC > > >=20 > > > Dropping and retaking the lock in here is an anti-pattern that > > > should be avoided. I suggest we are better off in the long run if > > > the caller does not need to take the RCU read lock, but instead, > > > nfsd_open_local_fh takes it right here just for the rcu_dereference. >=20 > I thought so too when I first saw how Neil approached fixing this to > be safe. It was only after putting further time to it (and having the > benefit of being so close to all this) that I realized the nuance at > play (please see my reply to Jeff below for the nuance I'm speaking > of).=20 >=20 > > >=20 > > > OTOH, Why drop the lock before calling nfsd_file_acquire_local()? > > > The RCU read lock can safely be taken more than once in succession. > > >=20 > > > Let's rethink the locking strategy. > > >=20 >=20 > Yes, _that_ is a very valid point. I did wonder the same: it seems > perfectly fine to simply retain the RCU throughout the entirety of > nfsd_open_local_fh(). >=20 Nope. nfsd_file_do_acquire can allocate, so you can't hold the rcu_read_lock over the whole thing. > > Agreed. The only caller does this: > >=20 > > rcu_read_lock(); > > if (!rcu_access_pointer(uuid->net)) { > > rcu_read_unlock(); > > return ERR_PTR(-ENXIO); > > } > > localio =3D nfs_to.nfsd_open_local_fh(uuid, rpc_clnt, cred, > > nfs_fh, fmode); > > rcu_read_unlock(); > >=20 > > Maybe just move the check for uuid->net down into nfsd_open_local_fh, > > and it can acquire the rcu_read_lock for itself? >=20 > No, sorry we cannot. The call to nfs_to.nfsd_open_local_fh (which is > a symbol provided by nfsd) is only safe if the RCU protected pre-check > shows the uuid->net valid. Ouch, ok. --=20 Jeff Layton