linux-kernel - Re: [PATCH v11 2/6] arm64: idle: Tag the arm64 idle functions as _

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Date:   Tue, 29 Aug 2023 16:08:06 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kgdb-bugreport@...ts.sourceforge.net,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        linux-perf-users@...r.kernel.org,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        Chen-Yu Tsai <wens@...e.org>,
        linux-arm-kernel@...ts.infradead.org, ito-yuichi@...itsu.com,
        Stephen Boyd <swboyd@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Guo Ren <guoren@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 2/6] arm64: idle: Tag the arm64 idle functions as __cpuidle

On Thu, 24 Aug 2023 at 21:03, Douglas Anderson <dianders@...omium.org> wrote:
>
> As per the (somewhat recent) comment before the definition of
> `__cpuidle`, the tag is like `noinstr` but also marks a function so it
> can be identified by cpu_in_idle(). Let's add these markings to arm64
> cpuidle functions
>
> With this change we get useful backtraces like:
>
>   NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98
>
> instead of useless backtraces when dumping all processors using
> nmi_cpu_backtrace().
>
> NOTE: this patch won't make cpu_in_idle() work perfectly for arm64,
> but it doesn't hurt and does catch some cases. Specifically an example
> that wasn't caught in my testing looked like this:
>
>  gic_cpu_sys_reg_init+0x1f8/0x314
>  gic_cpu_pm_notifier+0x40/0x78
>  raw_notifier_call_chain+0x5c/0x134
>  cpu_pm_notify+0x38/0x64
>  cpu_pm_exit+0x20/0x2c
>  psci_enter_idle_state+0x48/0x70
>  cpuidle_enter_state+0xb8/0x260
>  cpuidle_enter+0x44/0x5c
>  do_idle+0x188/0x30c
>
> Acked-by: Mark Rutland <mark.rutland@....com>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>

Acked-by: Sumit Garg <sumit.garg@...aro.org>

-Sumit

> Changes in v11:
> - Updated commit message as per Stephen.
>
> Changes in v9:
> - Added to commit message that this doesn't catch all cases.
>
> Changes in v8:
> - "Tag the arm64 idle functions as __cpuidle" new for v8
>
>  arch/arm64/kernel/idle.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/idle.c b/arch/arm64/kernel/idle.c
> index c1125753fe9b..05cfb347ec26 100644
> --- a/arch/arm64/kernel/idle.c
> +++ b/arch/arm64/kernel/idle.c
> @@ -20,7 +20,7 @@
>   *     ensure that interrupts are not masked at the PMR (because the core will
>   *     not wake up if we block the wake up signal in the interrupt controller).
>   */
> -void noinstr cpu_do_idle(void)
> +void __cpuidle cpu_do_idle(void)
>  {
>         struct arm_cpuidle_irq_context context;
>
> @@ -35,7 +35,7 @@ void noinstr cpu_do_idle(void)
>  /*
>   * This is our default idle handler.
>   */
> -void noinstr arch_cpu_idle(void)
> +void __cpuidle arch_cpu_idle(void)
>  {
>         /*
>          * This should do all the clock switching and wait for interrupt
> --
> 2.42.0.rc1.204.g551eb34607-goog
>