linux-kernel - Re: [PATCH v5 1/5] bug/kunit: Core support for suppressing warning backtraces

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Message-ID: <8C5E309E-03E5-4353-8515-67A53EC6C9E3@kernel.org>
Date: Sat, 31 May 2025 06:51:50 -0700
From: Kees Cook <kees@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
CC: Alessandro Carminati <acarmina@...hat.com>, linux-kselftest@...r.kernel.org,
 Dan Carpenter <dan.carpenter@...aro.org>,
 Daniel Diaz <daniel.diaz@...aro.org>, David Gow <davidgow@...gle.com>,
 Arthur Grillo <arthurgrillo@...eup.net>,
 Brendan Higgins <brendan.higgins@...ux.dev>,
 Naresh Kamboju <naresh.kamboju@...aro.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Maxime Ripard <mripard@...nel.org>,
 Ville Syrjala <ville.syrjala@...ux.intel.com>,
 Daniel Vetter <daniel@...ll.ch>, Guenter Roeck <linux@...ck-us.net>,
 Alessandro Carminati <alessandro.carminati@...il.com>,
 Jani Nikula <jani.nikula@...el.com>,
 Jeff Johnson <jeff.johnson@....qualcomm.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Shuah Khan <skhan@...uxfoundation.org>,
 Linux Kernel Functional Testing <lkft@...aro.org>,
 dri-devel@...ts.freedesktop.org, kunit-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v5 1/5] bug/kunit: Core support for suppressing warning backtraces



On May 31, 2025 3:23:04 AM PDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Fri, May 30, 2025 at 10:48:47AM -0700, Kees Cook wrote:
>> On Fri, May 30, 2025 at 04:01:40PM +0200, Peter Zijlstra wrote:
>> > I'm not really concerned with performance here, but more with the size
>> > of the code emitted by WARN_ONCE(). There are a *ton* of WARN sites,
>> > while only one report_bug() and printk().
>> > 
>> > The really offensive thing is that this is for a feature most nobody
>> > will ever need :/
>> 
>> Well, it won't be enabled often -- this reminds me of ftrace: it needs
>> to work, but it'll be off most of the time.
>
>Well, ftrace is useful, but when would I *ever* care about this stuff? I
>can't operate kunit, don't give a crap about kunit, and if I were to
>magically run it, I would be more than capable of ignoring WARNs.

It's not for you, then. :) I can't operate ftrace, but I use kunit almost daily. Ignoring WARNs makes this much nicer, and especially for CIs.

>Cleaned it up a little bit... I'll add some comments on later :-)
>
>I also need to go fix WARN_ONCE(), at least for the n<=2 cases that can
>use BUGFLAG_ONCE now.

Cool! I'll expand the WARN tests in LKDTM so we can get wider behavioral and architectural coverage.

-Kees


-- 
Kees Cook