linux-kernel - Re: [PATCH] arm64: watchdog_hld: provide arm_pmu_irq_is

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Message-ID: <CAD=FV=XrTVVEP8gLx3e7Sqa_3fod3Ox79Ao5fk3S_ORH7jHS9Q@mail.gmail.com>
Date:   Mon, 22 May 2023 07:31:41 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pingfan Liu <kernelfans@...il.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Petr Mladek <pmladek@...e.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: watchdog_hld: provide arm_pmu_irq_is_nmi stub

Hi,

On Mon, May 22, 2023 at 4:49 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> The newly added arch_perf_nmi_is_available() function fails to build
> when CONFIG_ARM_PMU is disabled:
>
> arch/arm64/kernel/watchdog_hld.c: In function 'arch_perf_nmi_is_available':
> arch/arm64/kernel/watchdog_hld.c:35:16: error: implicit declaration of function 'arm_pmu_irq_is_nmi' [-Werror=implicit-function-declaration]
>    35 |         return arm_pmu_irq_is_nmi();
>
> As it turns out, there is only one caller for that function anyway,
> in the same file as the __weak definition, and this can only be called
> if CONFIG_ARM_PMU is also enabled.
>
> I tried a number of variants, but everything ended up with more
> complexity from having both the __weak function and one or more
> added #ifdef. Keeping it in watchdog_perf.c is a small layering
> violation but otherwise the most robust.

Sorry for the breakage!

The intention here is that turning on CONFIG_HARDLOCKUP_DETECTOR_PERF
doesn't make any sense if the PMU is not enabled. In that sense, maybe
a better option would be to just fix this in Kconfig? What about going
into `arch/arm64/Kconfig` and instead of:

select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS && HAVE_PERF_EVENTS_NMI

We do:

select HAVE_HARDLOCKUP_DETECTOR_PERF if PERF_EVENTS &&
HAVE_PERF_EVENTS_NMI && HW_PERF_EVENTS

It looks like HW_PERF_EVENTS is a synonym for ARM_PMU and that's the
same symbol used to include the needed definition.

Making that change seems to fix the compile error and has the added
benefit that enabling CONFIG_HARDLOCKUP_DETECTOR will automatically
choose the "buddy" backend when CONFIG_ARM_PMU isn't turned on.

-Doug