linux-kernel - Re: [PATCH arm] Use common outgoing-CPU-notification code

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Date:   Mon, 17 Jun 2019 12:58:19 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     linux@....linux.org.uk, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH arm] Use common outgoing-CPU-notification code

On Tue, Jun 11, 2019 at 12:24:10PM -0700, Paul E. McKenney wrote:
> This commit removes the open-coded CPU-offline notification with new
> common code.  In particular, this change avoids calling scheduler code
> using RCU from an offline CPU that RCU is ignoring.  This is a minimal
> change.  A more intrusive change might invoke the cpu_check_up_prepare()
> and cpu_set_state_online() functions at CPU-online time, which would
> allow onlining throw an error if the CPU did not go offline properly.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Mark Rutland <mark.rutland@....com>
> Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>

FWIW:

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

On the assumption that Russell is ok with this, I think this should be
dropped into the ARM patch system [1].

Paul, are you familiar with that, or would you prefer that someone else
submits the patch there? I can do so if you'd like.

Thanks,
Mark.

[1] https://www.armlinux.org.uk/developer/patches/info.php

> 
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index ebc53804d57b..8687d619260f 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -267,15 +267,13 @@ int __cpu_disable(void)
>  	return 0;
>  }
>  
> -static DECLARE_COMPLETION(cpu_died);
> -
>  /*
>   * called on the thread which is asking for a CPU to be shutdown -
>   * waits until shutdown has completed, or it is timed out.
>   */
>  void __cpu_die(unsigned int cpu)
>  {
> -	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) {
> +	if (!cpu_wait_death(cpu, 5)) {
>  		pr_err("CPU%u: cpu didn't die\n", cpu);
>  		return;
>  	}
> @@ -322,7 +320,7 @@ void arch_cpu_idle_dead(void)
>  	 * this returns, power and/or clocks can be removed at any point
>  	 * from this CPU and its cache by platform_cpu_kill().
>  	 */
> -	complete(&cpu_died);
> +	(void)cpu_report_death();
>  
>  	/*
>  	 * Ensure that the cache lines associated with that completion are
>