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Message-ID: <20230929-keimt-umspannen-bfd12d2c2033@brauner> Date: Fri, 29 Sep 2023 11:32:49 +0200 From: Christian Brauner <brauner@...nel.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Jeff Layton <jlayton@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, David Sterba <dsterba@...e.cz>, Amir Goldstein <amir73il@...il.com>, Theodore Ts'o <tytso@....edu>, Eric Biederman <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, Jeremy Kerr <jk@...abs.org>, Arnd Bergmann <arnd@...db.de>, Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>, Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, Joel Fernandes <joel@...lfernandes.org>, Carlos Llamas <cmllamas@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>, Mattia Dongili <malattia@...ux.it>, Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>, Brad Warrum <bwarrum@...ux.ibm.com>, Ritu Agarwal <rituagar@...ux.ibm.com>, Hans de Goede <hdegoede@...hat.com>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, Mark Gross <markgross@...nel.org>, Jiri Slaby <jirislaby@...nel.org>, Eric Van Hensbergen <ericvh@...nel.org>, Latchesar Ionkov <lucho@...kov.net>, Dominique Martinet <asmadeus@...ewreck.org>, Christian Schoenebeck <linux_oss@...debyte.com>, David Sterba <dsterba@...e.com>, David Howells <dhowells@...hat.com>, Marc Dionne <marc.dionne@...istor.com>, Ian Kent <raven@...maw.net>, Luis de Bethencourt <luisbg@...nel.org>, Salah Triki <salah.triki@...il.com>, "Tigran A. Aivazian" <aivazian.tigran@...il.com>, Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>, Xiubo Li <xiubli@...hat.com>, Ilya Dryomov <idryomov@...il.com>, Jan Harkes <jaharkes@...cmu.edu>, coda@...cmu.edu, Joel Becker <jlbec@...lplan.org>, Christoph Hellwig <hch@....de>, Nicolas Pitre <nico@...xnic.net>, "Rafael J. Wysocki" <rafael@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, Gao Xiang <xiang@...nel.org>, Chao Yu <chao@...nel.org>, Yue Hu <huyue2@...lpad.com>, Jeffle Xu <jefflexu@...ux.alibaba.com>, Namjae Jeon <linkinjeon@...nel.org>, Sungjong Seo <sj1557.seo@...sung.com>, Jan Kara <jack@...e.com>, Andreas Dilger <adilger.kernel@...ger.ca>, Jaegeuk Kim <jaegeuk@...nel.org>, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>, Christoph Hellwig <hch@...radead.org>, Miklos Szeredi <miklos@...redi.hu>, Bob Peterson <rpeterso@...hat.com>, Andreas Gruenbacher <agruenba@...hat.com>, Richard Weinberger <richard@....at>, Anton Ivanov <anton.ivanov@...bridgegreys.com>, Johannes Berg <johannes@...solutions.net>, Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>, Mike Kravetz <mike.kravetz@...cle.com>, Muchun Song <muchun.song@...ux.dev>, Jan Kara <jack@...e.cz>, David Woodhouse <dwmw2@...radead.org>, Dave Kleikamp <shaggy@...nel.org>, Tejun Heo <tj@...nel.org>, Trond Myklebust <trond.myklebust@...merspace.com>, Anna Schumaker <anna@...nel.org>, Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>, Olga Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>, Ryusuke Konishi <konishi.ryusuke@...il.com>, Anton Altaparmakov <anton@...era.com>, Konstantin Komarov <almaz.alexandrovich@...agon-software.com>, Mark Fasheh <mark@...heh.com>, Joseph Qi <joseph.qi@...ux.alibaba.com>, Bob Copeland <me@...copeland.com>, Mike Marshall <hubcap@...ibond.com>, Martin Brandenburg <martin@...ibond.com>, Luis Chamberlain <mcgrof@...nel.org>, Iurii Zaikin <yzaikin@...gle.com>, Tony Luck <tony.luck@...el.com>, "Guilherme G. Piccoli" <gpiccoli@...lia.com>, Anders Larsen <al@...rsen.net>, Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.com>, Ronnie Sahlberg <lsahlber@...hat.com>, Shyam Prasad N <sprasad@...rosoft.com>, Sergey Senozhatsky <senozhatsky@...omium.org>, Phillip Lougher <phillip@...ashfs.org.uk>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Evgeniy Dushistov <dushistov@...l.ru>, Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>, Damien Le Moal <dlemoal@...nel.org>, Naohiro Aota <naohiro.aota@....com>, Johannes Thumshirn <jth@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Hugh Dickins <hughd@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, John Johansen <john.johansen@...onical.com>, Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, Stephen Smalley <stephen.smalley.work@...il.com>, Eric Paris <eparis@...isplace.org>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org, platform-driver-x86@...r.kernel.org, linux-rdma@...r.kernel.org, linux-serial@...r.kernel.org, linux-usb@...r.kernel.org, v9fs@...ts.linux.dev, linux-afs@...ts.infradead.org, autofs@...r.kernel.org, linux-btrfs@...r.kernel.org, ceph-devel@...r.kernel.org, codalist@...a.cs.cmu.edu, linux-efi@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, gfs2@...ts.linux.dev, linux-um@...ts.infradead.org, linux-mtd@...ts.infradead.org, jfs-discussion@...ts.sourceforge.net, linux-nfs@...r.kernel.org, linux-nilfs@...r.kernel.org, linux-ntfs-dev@...ts.sourceforge.net, ntfs3@...ts.linux.dev, ocfs2-devel@...ts.linux.dev, linux-karma-devel@...ts.sourceforge.net, devel@...ts.orangefs.org, linux-unionfs@...r.kernel.org, linux-hardening@...r.kernel.org, reiserfs-devel@...r.kernel.org, linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org, linux-trace-kernel@...r.kernel.org, linux-xfs@...r.kernel.org, bpf@...r.kernel.org, netdev@...r.kernel.org, apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org, selinux@...r.kernel.org Subject: Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode On Thu, Sep 28, 2023 at 10:41:34AM -0700, Linus Torvalds wrote: > On Thu, 28 Sept 2023 at 04:06, Jeff Layton <jlayton@...nel.org> wrote: > > > > Move i_blocks up above the i_lock, which moves the new 4 byte hole to > > just after the timestamps, without changing the size of the structure. > > I'm sure others have mentioned this, but 'struct inode' is marked with > __randomize_layout, so the actual layout may end up being very > different. > > I'm personally not convinced the whole structure randomization is > worth it - it's easy enough to figure out for any distro kernel since > the seed has to be the same across machines for modules to work, so > even if the seed isn't "public", any layout is bound to be fairly > easily discoverable. > > So the whole randomization only really works for private kernel > builds, and it adds this kind of pain where "optimizing" the structure > layout is kind of pointless depending on various options. > > I certainly *hope* no distro enables that pointless thing, but it's a worry. They don't last we checked. Just last cycle we moved stuff in struct file around to optimize things and we explicitly said we don't give a damn about struct randomization. Anyone who enables this will bleed performance pretty badly, I would reckon.
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