linux-kernel - Re: Removing Mandatory Locks

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Message-ID: <20210819200323.GA13017@1wt.eu>
Date:   Thu, 19 Aug 2021 22:03:23 +0200
From:   Willy Tarreau <w@....eu>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Rodrigo Campos <rodrigo@...volk.io>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.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>,
        "H. Peter Anvin" <hpa@...or.com>,
        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>,
        Kees Cook <keescook@...omium.org>,
        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>,
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        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

On Thu, Aug 19, 2021 at 03:18:15PM -0400, Jeff Layton wrote:
> On Wed, 2021-08-18 at 11:34 +0200, Rodrigo Campos wrote:
> > On Tue, Aug 17, 2021 at 6:49 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> > > 
> > > Matthew Wilcox <willy@...radead.org> writes:
> > > 
> > > > On Fri, Aug 13, 2021 at 05:49:19PM -0700, Andy Lutomirski wrote:
> > > > > [0] we have mandatory locks, too. Sigh.
> > > > 
> > > > I'd love to remove that.  Perhaps we could try persuading more of the
> > > > distros to disable the CONFIG option first.
> > > 
> > > Yes.  The support is disabled in RHEL8.
> > 
> > If it helps, it seems to be enabled on the just released debian stable:
> >     $ grep CONFIG_MANDATORY_FILE_LOCKING /boot/config-5.10.0-8-amd64
> >     CONFIG_MANDATORY_FILE_LOCKING=y
> > 
> > Also the new 5.13 kernel in experimental has it too:
> >     $ grep CONFIG_MANDATORY_FILE_LOCKING /boot/config-5.13.0-trunk-amd64
> >     CONFIG_MANDATORY_FILE_LOCKING=y
> 
> A pity. It would have been nice if they had turned it off a while ago. I
> guess I should have done more outreach at the time. Sigh...

Would it be acceptable to add a warning when MS_MANDLOCK is passed to
mount() and backport this to stable kernels in order to get reports
of any such use in a reasonably short time ? Anyway it sounds
important to at least warn about deprecation.

Willy