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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Mon, 23 Aug 2021 09:55:57 +0200
Message-ID: <CAMuHMdVWC9=TtFG7=SmN+KQ=phh1MqNqgLFbrWXr9XsDv-Sp5Q@mail.gmail.com>
Subject: Re: Removing Mandatory Locks
To:     David Laight <David.Laight@aculab.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jeff Layton <jlayton@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Matthew Wilcox <willy@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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On Fri, Aug 20, 2021 at 10:30 AM David Laight <David.Laight@aculab.com> wrote:
> From: Linus Torvalds
> > Sent: 19 August 2021 23:33
> >
> > On Thu, Aug 19, 2021 at 2:43 PM Jeff Layton <jlayton@kernel.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@linux-foundation.org> wrote:
> On Fri, Aug 20, 2021 at 6:43 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Thu, 19 Aug 2021 15:32:31 -0700
> > Linus Torvalds <torvalds@linux-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@linux-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