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References: <20230616150618.6073-1-pmladek@suse.com> <20230616150618.6073-3-pmladek@suse.com>
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From:   Doug Anderson <dianders@chromium.org>
Date:   Fri, 16 Jun 2023 09:47:47 -0700
Message-ID: <CAD=FV=VPhpZyJO=U3NGy1RZbmAQS_xEoDs-K2HawJYb=UHaUww@mail.gmail.com>
Subject: Re: [PATCH v2 2/6] watchdog/hardlockup: Make the config checks more straightforward
To:     Petr Mladek <pmladek@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        kgdb-bugreport@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        Nicholas Piggin <npiggin@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        sparclinux@vger.kernel.org,
        "David S . Miller" <davem@davemloft.net>,
        linux-perf-users@vger.kernel.org
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Hi,

On Fri, Jun 16, 2023 at 8:07=E2=80=AFAM Petr Mladek <pmladek@suse.com> wrot=
e:
>
> There are four possible variants of hardlockup detectors:
>
>   + buddy: available when SMP is set.
>
>   + perf: available when HAVE_HARDLOCKUP_DETECTOR_PERF is set.
>
>   + arch-specific: available when HAVE_HARDLOCKUP_DETECTOR_ARCH is set.
>
>   + sparc64 special variant: available when HAVE_NMI_WATCHDOG is set
>         and HAVE_HARDLOCKUP_DETECTOR_ARCH is not set.
>
> The check for the sparc64 variant is more complicated because
> HAVE_NMI_WATCHDOG is used to #ifdef code used by both arch-specific
> and sparc64 specific variant. Therefore it is automatically
> selected with HAVE_HARDLOCKUP_DETECTOR_ARCH.
>
> This complexity is partly hidden in HAVE_HARDLOCKUP_DETECTOR_NON_ARCH.
> It reduces the size of some checks but it makes them harder to follow.
>
> Finally, the other temporary variable HARDLOCKUP_DETECTOR_NON_ARCH
> is used to re-compute HARDLOCKUP_DETECTOR_PERF/BUDDY when the global
> HARDLOCKUP_DETECTOR switch is enabled/disabled.
>
> Make the logic more straightforward by the following changes:
>
>   + Better explain the role of HAVE_HARDLOCKUP_DETECTOR_ARCH and
>     HAVE_NMI_WATCHDOG in comments.
>
>   + Add HAVE_HARDLOCKUP_DETECTOR_BUDDY so that there is separate
>     HAVE_* for all four hardlockup detector variants.
>
>     Use it in the other conditions instead of SMP. It makes it
>     clear that it is about the buddy detector.
>
>   + Open code HAVE_HARDLOCKUP_DETECTOR_NON_ARCH in HARDLOCKUP_DETECTOR
>     and HARDLOCKUP_DETECTOR_PREFER_BUDDY. It helps to understand
>     the conditions between the four hardlockup detector variants.
>
>   + Define the exact conditions when HARDLOCKUP_DETECTOR_PERF/BUDDY
>     can be enabled. It explains the dependency on the other
>     hardlockup detector variants.
>
>     Also it allows to remove HARDLOCKUP_DETECTOR_NON_ARCH by using "imply=
".
>     It triggers re-evaluating HARDLOCKUP_DETECTOR_PERF/BUDDY when
>     the global HARDLOCKUP_DETECTOR switch is changed.
>
>   + Add dependency on HARDLOCKUP_DETECTOR so that the affected variables
>     disappear when the hardlockup detectors are disabled.
>
>     Another nice side effect is that HARDLOCKUP_DETECTOR_PREFER_BUDDY
>     value is not preserved when the global switch is disabled.
>     The user has to make the decision again when it gets re-enabled.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> ---
>  arch/Kconfig      | 23 +++++++++++++-----
>  lib/Kconfig.debug | 62 +++++++++++++++++++++++++++--------------------
>  2 files changed, 53 insertions(+), 32 deletions(-)

While I'd still paint the bikeshed a different color and organize the
dependencies a little differently, as discussed in your v1 post, this
is still OK w/ me.

Reviewed-by: Douglas Anderson <dianders@chromium.org>