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Message-ID: <CAHk-=wgD-SNxB=2iCurEoP=RjrciRgLtXZ7R_DejK+mXF2etfg@mail.gmail.com>
Date:   Thu, 19 Aug 2021 13:31:35 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jeff Layton <jlayton@...nel.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>,
        "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>,
        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

On Thu, Aug 19, 2021 at 1:18 PM Jeff Layton <jlayton@...nel.org> wrote:
>
> Now that I think about it a little more, I actually did get one
> complaint a few years ago:
>
> Someone had upgraded from an earlier distro that supported the -o mand
> mount option to a later one that had disabled it, and they had an (old)
> fstab entry that specified it.

Hmm. We might be able to turn the "return -EINVAL" into just a warning.

Yes, yes, currently if you turn off CONFIG_MANDATORY_FILE_LOCKING, we
already do that

        VFS: "mand" mount option not supported

warning print, but then we fail the mount.

If CONFIG_MANDATORY_FILE_LOCKING goes away entirely, it might make
sense to turn that warning into something bigger, but then let the
mount continue - since now that "mand" flag would be purely a legacy
thing.

And yes, if we do that, we'd want the warning to be a big ugly thing,
just to make people very aware of it happening. Right now it's a
one-liner that is easy to miss, and the "oh, the mount failed" is the
thing that hopefully informs people about the fact that they need to
enable CONFIG_MANDATORY_FILE_LOCKING.

The logic being that if you can no longer enable mandatory locking in
the kernel, the current hard failure seems overly aggressive (and
might cause boot failures and inability to fix/report things when it
possibly keeps you from using the system at all).

              Linus

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