linux-kernel - Re: Removing Mandatory Locks

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Date:   Fri, 20 Aug 2021 17:29:30 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     "H. Peter Anvin" <hpa@...or.com>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        David Hildenbrand <david@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mike Rapoport <rppt@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Michel Lespinasse <walken@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Huang Ying <ying.huang@...el.com>,
        Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
        Kevin Brodsky <Kevin.Brodsky@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Shawn Anastasio <shawn@...stas.io>,
        Steven Price <steven.price@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jens Axboe <axboe@...nel.dk>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Peter Xu <peterx@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Thomas Cedeno <thomascedeno@...gle.com>,
        Collin Fijalkovich <cfijalkovich@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Chengguang Xu <cgxu519@...ernel.net>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        "linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "<linux-fsdevel@...r.kernel.org>" <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Florian Weimer <fweimer@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: Removing Mandatory Locks

No, Windows has deny-mode locking at open time, but the kernel's
mandatory locks are enforced during read/write (which is why they are
such a pain). Samba will not miss these at all.

If we want something to provide windows-like semantics, we'd probably
want to start with something like Pavel Shilovsky's O_DENY_* patches.

-- Jeff

On Fri, 2021-08-20 at 12:17 -0700, H. Peter Anvin wrote:
> I thought the main user was Samba and/or otherwise providing file service for M$ systems?
> 
> On August 20, 2021 9:30:31 AM PDT, Kees Cook <keescook@...omium.org> wrote:
> > On Thu, Aug 19, 2021 at 12:15:08PM -0700, Linus Torvalds wrote:
> > > On Thu, Aug 19, 2021 at 11:39 AM Jeff Layton <jlayton@...nel.org> wrote:
> > > > 
> > > > I'm all for ripping it out too. It's an insane interface anyway.
> > > > 
> > > > I've not heard a single complaint about this being turned off in
> > > > fedora/rhel or any other distro that has this disabled.
> > > 
> > > I'd love to remove it, we could absolutely test it. The fact that
> > > several major distros have it disabled makes me think it's fine.
> > 
> > FWIW, it is now disabled in Ubuntu too:
> > 
> > https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/impish/commit/?h=master-next&id=f3aac5e47789cbeb3177a14d3d2a06575249e14b
> > 
> > > But as always, it would be good to check Android.
> > 
> > It looks like it's enabled (checking the Pixel 4 kernel image), but it's
> > not specifically mentioned in any of the build configs that are used to
> > construct the image, so I think this is just catching the "default y". I
> > expect it'd be fine to turn this off.
> > 
> > I will ask around to see if it's actually used.
> > 
> 

-- 
Jeff Layton <jlayton@...nel.org>