linux-kernel - Re: [PATCH] bug: Introduce CONFIG_DEBUG_BUGVERBOSE

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Message-ID: <CAHk-=wg_BRnCs8o5vEjK_zDuc0KJ-z9bvq5845jKv+7UduS4hQ@mail.gmail.com>
Date: Tue, 25 Mar 2025 10:48:49 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-tip-commits@...r.kernel.org, Shrikanth Hegde <sshegde@...ux.ibm.com>, 
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, 
	Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, 
	Valentin Schneider <vschneid@...hat.com>, x86@...nel.org
Subject: Re: [PATCH] bug: Introduce CONFIG_DEBUG_BUGVERBOSE_EXTRA=y to also
 log warning conditions

 On Tue, 25 Mar 2025 at 05:36, Peter Zijlstra <peterz@...radead.org> wrote:
>
> The problem with WARN() is that it is a format string, which must be
> filled out in situ. Resulting in calls to snprintf() and arguments and
> whatnot.

A fair number of warnings do want the format string, so that you can
print out more information about what went wrong if the warning
triggered.

That said, I do think that the "just give a fixed string that is the
warning condition" is probably the right thing 90% of the time, and is
the much simpler interface both to use and causes much less code
(exactly because it's just a single hardcoded string at compile time).

So I think we end up wanting both.

But I *don't* like Ingo's suggestion of DEBUG_BUGVERBOSE_EXTRA,
because it does that "both" by making the simple case complicated.

How about going a different route instead? Right now we have that
CONFIG_DEBUG_BUGVERBOSE thing which adds the file name and line number
information. That has been very good.

But maybe that should be extended to also always take the compile-time
'#condition' string?

So then all warnings would have the warning condition string (assuming
you end up enabling DEBUG_BUGVERBOSE, of course, which I think
everybody pretty much does). With no extra code.

And then the _dynamic_ string - and associated code generation - would
be only for when you want to print out the actual values that caused
the warning.

Hmm?

             Linus