linux-kernel - Re: [PATCH v9 2/7] arm64: idle: Tag the arm64 idle functions as _

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Date:   Mon, 7 Aug 2023 10:52:09 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Marc Zyngier <maz@...nel.org>,
        linux-perf-users@...r.kernel.org, ito-yuichi@...itsu.com,
        Chen-Yu Tsai <wens@...e.org>, Ard Biesheuvel <ardb@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        kgdb-bugreport@...ts.sourceforge.net,
        Masayoshi Mizuma <msys.mizuma@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Gautham R. Shenoy" <gautham.shenoy@....com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 2/7] arm64: idle: Tag the arm64 idle functions as
 __cpuidle

On Thu, Jun 01, 2023 at 02:31:46PM -0700, Douglas Anderson 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'a add this.
> 
> After doing this then when we dump stack traces of all processors
> using nmi_cpu_backtrace() then instead of getting useless backtraces
> we get things like:
> 
>   NMI backtrace for cpu N skipped: idling at cpu_do_idle+0x94/0x98
> 
> 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
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

I don't have strong feelings either way for this, so:

Acked-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.

> ---
> 
> 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
> -- 
> 2.41.0.rc2.161.g9c6817b8e7-goog
>