linux-kernel - Re: [PATCH v4 06/14] x86: Add support for suppressing warning backtraces

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Message-ID: <20250402074219.GP5880@noisy.programming.kicks-ass.net>
Date: Wed, 2 Apr 2025 09:42:19 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Alessandro Carminati <acarmina@...hat.com>,
	linux-kselftest@...r.kernel.org, David Airlie <airlied@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Maíra Canal <mcanal@...lia.com>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	Kees Cook <keescook@...omium.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>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Maxime Ripard <mripard@...nel.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Alessandro Carminati <alessandro.carminati@...il.com>,
	Jani Nikula <jani.nikula@...el.com>,
	dri-devel@...ts.freedesktop.org, kunit-dev@...glegroups.com,
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, loongarch@...ts.linux.dev, x86@...nel.org,
	Linux Kernel Functional Testing <lkft@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 06/14] x86: Add support for suppressing warning
 backtraces

On Tue, Apr 01, 2025 at 10:53:46AM -0700, Guenter Roeck wrote:

> > > @@ -92,7 +102,8 @@ do {								\
> > >   do {								\
> > >   	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
> > >   	instrumentation_begin();				\
> > > -	_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE(1b));	\
> > > +	if (!KUNIT_IS_SUPPRESSED_WARNING(__func__))			\
> > > +		_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE(1b));	\
> > >   	instrumentation_end();					\
> > >   } while (0)
> > 
> > NAK, this grows the BUG site for now appreciable reason.
> 
> Only if CONFIG_KUNIT_SUPPRESS_BACKTRACE is enabled. Why does that warrant a NACK ?

And isn't that something distros will want enabled? All I'm seeing is
bloating every single UD2 site, and no real justification. As Josh said,
this should be done on the other side of the trap if at all.