linux-kernel - Re: [PATCH 00/50] Add log level to show

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Date:   Thu, 7 Nov 2019 08:27:29 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Whitcroft <apw@...onical.com>,
        Joe Perches <joe@...ches.com>,
        Dmitry Safonov <dima@...sta.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 00/50] Add log level to show_stack()

Hi Russell,

(reduced CC list)

On Thu, Nov 7, 2019 at 12:28 AM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
> On Wed, Nov 06, 2019 at 09:34:40PM +0100, Peter Zijlstra wrote:
> > I suppose I'm surprised there are backtraces that are not important.
> > Either badness happened and it needs printing, or the user asked for it
> > and it needs printing.
>
> Or utterly meaningless.
>
> > Perhaps we should be removing backtraces if they're not important
> > instead of allowing to print them as lower loglevels?
>
> Definitely!  WARN_ON() is well overused - and as is typical, used
> without much thought.  Bound to happen after Linus got shirty about
> BUG_ON() being over used.  Everyone just grabbed the next nearest thing
> to assert().

Which is what checkpatch.pl suggests...

> As a kind of example, I've recently come across one WARN_ON() in a
> driver subsystem (that shall remain nameless at the moment) which very
> likely has multiple different devices on a platform.  The WARN_ON()
> triggers as a result of a problem with the hardware, but because it's a
> WARN_ON(), you've no idea which device has a problem.  The backtrace is
> mostly meaningless.  So you know that a problem has occurred, but the
> kernel prints *useless* backtrace to let you know, and totally omits
> the *useful* information.

So that callsite should be converted to use dev_WARN(), with a suitable
message.

Perhaps checkpatch should be updated, to suggest {,dev_}WARN()
instead of WARN_ON(), and add a check for the latter, too?

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