Date:   Mon, 23 Aug 2021 09:55:57 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jeff Layton <jlayton@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        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>,
        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 Fri, Aug 20, 2021 at 10:30 AM David Laight <David.Laight@...lab.com> wrote:
> From: Linus Torvalds
> > Sent: 19 August 2021 23:33
> >
> > On Thu, Aug 19, 2021 at 2:43 PM Jeff Layton <jlayton@...nel.org> wrote:
> > >
> > > What sort of big, ugly warning did you have in mind?
> >
> > I originally thought WARN_ON_ONCE() just to get the distro automatic
> > error handling involved, but it would probably be a big problem for
> > the people who end up having panic-on-warn or something.
>
> Even panic-on-oops is a PITA.
> Took us weeks to realise that a customer system that was randomly
> rebooting was 'just' having a boring NULL pointer access.
>
> > So probably just a "make it a big box" thing that stands out, kind of
> > what lockdep etc does with
> >
> >         pr_warn("======...====\n");
> >
> > around the messages..

Do we really need more of these?
They take time to print (especially on serial
consoles) and increase kernel size.

What's wrong with using an appropriate KERN_*, and letting userspace
make sure the admin/user will see the message (see below)?

> >
> > I don't know if distros have some pattern we could use that would end
> > up being something that gets reported to the user?
>
> Will users even see it?
> A lot of recent distro installs try very hard to hide all the kernel
> messages.

Exactly.  E.g. Ubuntu doesn't show any kernel output during normal
operation.

On Fri, Aug 20, 2021 at 6:12 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Aug 20, 2021 at 6:43 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Thu, 19 Aug 2021 15:32:31 -0700
> > Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > >
> > > I don't know if distros have some pattern we could use that would end
> > > up being something that gets reported to the user?

> So what would be more interesting is if there's some distro support
> for showing kernel notifications..
>
> I see new notifications for calendar events, for devices that got
> mounted, for a lot of things - so I'm really wondering if somebody
> already perhaps had something for specially formatted kernel
> messages..

Isn't that what the old syslog and the new systemd are supposed to
handle in userspace?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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