Re: [PATCH v9 2/7] arm64: idle: Tag the arm64 idle functions as __cpuidle

From: Mark Rutland
Date: Mon Aug 07 2023 - 05:53:06 EST


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@xxxxxxxxxxxx>

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

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

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
>