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

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Message-ID: <202505281546.DB9D9029@keescook>
Date: Wed, 28 May 2025 15:47:42 -0700
From: Kees Cook <kees@...nel.org>
To: Alessandro Carminati <acarmina@...hat.com>
Cc: 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>,
	Peter Zijlstra <peterz@...radead.org>,
	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
Subject: Re: [PATCH v5 1/5] bug/kunit: Core support for suppressing warning
 backtraces

On Mon, May 26, 2025 at 01:27:51PM +0000, Alessandro Carminati wrote:
> Some unit tests intentionally trigger warning backtraces by passing bad
> parameters to kernel API functions. Such unit tests typically check the
> return value from such calls, not the existence of the warning backtrace.
> 
> Such intentionally generated warning backtraces are neither desirable
> nor useful for a number of reasons:
> - They can result in overlooked real problems.
> - A warning that suddenly starts to show up in unit tests needs to be
>   investigated and has to be marked to be ignored, for example by
>   adjusting filter scripts. Such filters are ad hoc because there is
>   no real standard format for warnings. On top of that, such filter
>   scripts would require constant maintenance.
> 
> Solve the problem by providing a means to identify and suppress specific
> warning backtraces while executing test code. Support suppressing multiple
> backtraces while at the same time limiting changes to generic code to the
> absolute minimum.
> 
> Implementation details:
> Check suppression directly in the `WARN()` Macros.
> This avoids the need for function symbol resolution or ELF section
> modification.
> Suppression is implemented directly in the `WARN*()` macros.
> 
> A helper function, `__kunit_is_suppressed_warning()`, is used to determine
> whether suppression applies. It is marked as `noinstr`, since some `WARN*()`
> sites reside in non-instrumentable sections. As it uses `strcmp`, a
> `noinstr` version of `strcmp` was introduced.
> The implementation is deliberately simple and avoids architecture-specific
> optimizations to preserve portability. Since this mechanism compares
> function names and is intended for test usage only, performance is not a
> primary concern.
> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>

I like this -- it's very simple, it doesn't need to be fast-path, so
a linear list walker with strcmp is fine. Nice!

Reviewed-by: Kees Cook <kees@...nel.org>

-- 
Kees Cook