linux-kernel - Re: [PATCH 4/7] watchdog/hardlockup: Enable HAVE_NMI

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Message-ID: <CAD=FV=VV3Y7KoZWPtZfmfRsUCftAgo_CLRDazrYSgbR2XJKf=g@mail.gmail.com>
Date:   Wed, 7 Jun 2023 16:36:35 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        sparclinux@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 4/7] watchdog/hardlockup: Enable HAVE_NMI_WATCHDOG only on sparc64

Hi,

On Wed, Jun 7, 2023 at 8:25 AM Petr Mladek <pmladek@...e.com> wrote:
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 13c6e596cf9e..57f15babe188 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -404,10 +404,9 @@ config HAVE_NMI_WATCHDOG
>         depends on HAVE_NMI
>         bool
>         help
> -         The arch provides its own hardlockup detector implementation instead
> +         Sparc64 provides its own hardlockup detector implementation instead
>           of the generic perf one.

It's a little weird to document generic things with the specifics of
the user. The exception, IMO, is when something is deprecated.
Personally, it would sound less weird to me to say something like:

The arch provides its own hardlockup detector implementation instead
of the generic perf one. This is a deprecated thing to do and kept
around until sparc64 provides a full hardlockup implementation or
moves to generic code.


> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index d201f5d3876b..4b4aa0f941f9 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1050,15 +1050,13 @@ config HAVE_HARDLOCKUP_DETECTOR_BUDDY
>  #      sparc64: has a custom implementation which is not using the common
>  #              hardlockup command line options and sysctl interface.
>  #
> -# Note that HAVE_NMI_WATCHDOG is used to distinguish the sparc64 specific
> -# implementaion. It is automatically enabled also for other arch-specific
> -# variants which set HAVE_HARDLOCKUP_DETECTOR_ARCH. It makes the check
> -# of avaialable and supported variants quite tricky.
> +# Note that HAVE_NMI_WATCHDOG is set when the sparc64 specific implementation
> +# is used.
>  #
>  config HARDLOCKUP_DETECTOR
>         bool "Detect Hard Lockups"
> -       depends on DEBUG_KERNEL && !S390
> -       depends on ((HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY) && !HAVE_NMI_WATCHDOG) || HAVE_HARDLOCKUP_DETECTOR_ARCH
> +       depends on DEBUG_KERNEL && !S390 && !HAVE_NMI_WATCHDOG
> +       depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_BUDDY || HAVE_HARDLOCKUP_DETECTOR_ARCH

If you add the "!HAVE_NMI_WATCHDOG" as a dependency to
HAVE_HARDLOCKUP_DETECTOR_BUDDY, as discussed in a previous patch, you
can skip adding it here.


>         imply HARDLOCKUP_DETECTOR_PERF
>         imply HARDLOCKUP_DETECTOR_BUDDY
>         select LOCKUP_DETECTOR
> @@ -1079,7 +1077,7 @@ config HARDLOCKUP_DETECTOR_PREFER_BUDDY
>         bool "Prefer the buddy CPU hardlockup detector"
>         depends on HARDLOCKUP_DETECTOR
>         depends on HAVE_HARDLOCKUP_DETECTOR_PERF && HAVE_HARDLOCKUP_DETECTOR_BUDDY
> -       depends on !HAVE_NMI_WATCHDOG
> +       depends on !HAVE_HARLOCKUP_DETECTOR_ARCH

Don't need this. Architectures never are allowed to define
HAVE_HARDLOCKUP_DETECTOR_PERF and HAVE_HARLOCKUP_DETECTOR_ARCH


>         default n
>         help
>           Say Y here to prefer the buddy hardlockup detector over the perf one.
> @@ -1096,7 +1094,7 @@ config HARDLOCKUP_DETECTOR_PERF
>         bool
>         depends on HARDLOCKUP_DETECTOR
>         depends on HAVE_HARDLOCKUP_DETECTOR_PERF && !HARDLOCKUP_DETECTOR_PREFER_BUDDY
> -       depends on !HAVE_NMI_WATCHDOG
> +       depends on !HAVE_HARDLOCKUP_DETECTOR_ARCH

Similarly, don't need this.


>         select HARDLOCKUP_DETECTOR_COUNTS_HRTIMER
>
>  config HARDLOCKUP_DETECTOR_BUDDY
> @@ -1104,7 +1102,7 @@ config HARDLOCKUP_DETECTOR_BUDDY
>         depends on HARDLOCKUP_DETECTOR
>         depends on HAVE_HARDLOCKUP_DETECTOR_BUDDY
>         depends on !HAVE_HARDLOCKUP_DETECTOR_PERF || HARDLOCKUP_DETECTOR_PREFER_BUDDY
> -       depends on !HAVE_NMI_WATCHDOG
> +       depends on !HAVE_HARDLOCKUP_DETECTOR_ARCH

Similarly, don't need this.


In general I don't object to splitting out HAVE_NMI_WATCHDOG from
HAVE_HARDLOCKUP_DETECTOR_ARCH.