linux-kernel - Re: [PATCH tip/core/rcu 7/9] arm64: Use common outgoing-CPU-notification code

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Date:	Thu, 21 May 2015 09:58:06 +0100
From:	Will Deacon <will.deacon@....com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"laijs@...fujitsu.com" <laijs@...fujitsu.com>,
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	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
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	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Catalin Marinas <Catalin.Marinas@....com>
Subject: Re: [PATCH tip/core/rcu 7/9] arm64: Use common
 outgoing-CPU-notification code

Hi Paul,

Sorry for being late on this one.

On Tue, May 12, 2015 at 10:50:05PM +0100, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> 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: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/kernel/smp.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

I don't have a better idea, so:

  Acked-by: Will Deacon <will.deacon@....com>

Is this queued via -tip already, or can we pick it into the arm64 tree
for 4.2?

Cheers,

Will

> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 2cb008177252..a899c1beff54 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -253,15 +253,13 @@ static int op_cpu_kill(unsigned int cpu)
>  	return cpu_ops[cpu]->cpu_kill(cpu);
>  }
>  
> -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_crit("CPU%u: cpu didn't die\n", cpu);
>  		return;
>  	}
> @@ -294,7 +292,7 @@ void cpu_die(void)
>  	local_irq_disable();
>  
>  	/* Tell __cpu_die() that this CPU is now safe to dispose of */
> -	complete(&cpu_died);
> +	(void)cpu_report_death();
>  
>  	/*
>  	 * Actually shutdown the CPU. This must never fail. The specific hotplug
> -- 
> 1.8.1.5
> 
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