linux-kernel - Re: WARNING: CPU: 27 PID: 7051 at lib/math/int_log.c:63 intlog2+0xaa/0xe0 at running int_log

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Message-ID: <202601071229.C721443D5@keescook>
Date: Wed, 7 Jan 2026 12:35:10 -0800
From: Kees Cook <kees@...nel.org>
To: Erhard Furtner <erhard_f@...lbox.org>
Cc: linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com,
	Alessandro Carminati <acarmina@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: WARNING: CPU: 27 PID: 7051 at lib/math/int_log.c:63
 intlog2+0xaa/0xe0 at running int_log_kunit test (v6.15-rc1)

On Tue, Jan 06, 2026 at 11:17:33PM +0100, Erhard Furtner wrote:
> Greetings!
> 
> Still getting this warning on kernel v6.18.3 and v6.19-rc4 when running
> int_log_kunit test via modprobe on my systems (x86_64, x86, ppc). This dmesg
> is from my Intel Core Ultra 7 265F system:
> 
> [...]
> KTAP version 1
> 1..1
>     KTAP version 1
>     # Subtest: math-int_log
>     # module: int_log_kunit
>     1..2
>         KTAP version 1
>         # Subtest: intlog2_test
> ------------[ cut here ]------------
> 1
> WARNING: lib/math/int_log.c:63 at intlog2+0x59/0x70, CPU#16:

This is:

        if (unlikely(value == 0)) {
                WARN_ON(1);
                return 0;
        }


> [...]
>  ? kthreads_online_cpu+0xf0/0xf0
>  ? kthreads_online_cpu+0xf0/0xf0
>  ret_from_fork_asm+0x11/0x20
>  </TASK>
> ---[ end trace 0000000000000000 ]---
>         ok 1 Log base 2 of 0

Whcih seems to be exactly what is being tested...

It seems like we have another case of needed to silence warnings under
kunit[1]. Alessandro and Peter, where does the linked series stand
currently?

-Kees

[1] https://lore.kernel.org/lkml/20250526132755.166150-1-acarmina@redhat.com/

-- 
Kees Cook