linux-kernel - Re: [PATCH arm 1/2] arm64: Use common outgoing-CPU-notification code

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Message-ID: <20150501150848.GC5381@linux.vnet.ibm.com>
Date:	Fri, 1 May 2015 08:08:48 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux@....linux.org.uk, mingo@...nel.org, will.deacon@....com
Subject: Re: [PATCH arm 1/2] arm64: Use common outgoing-CPU-notification code

On Thu, Apr 30, 2015 at 10:50:55AM +0100, Catalin Marinas wrote:
> Hi Paul,
> 
> On Thu, Apr 23, 2015 at 01:07:33PM -0700, Paul E. McKenney wrote:
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index 328b8ce4b007..6dc727a6e73e 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -252,15 +252,13 @@ 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;
> >  	}
> > @@ -293,7 +291,7 @@ 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
> 
> Are these functions are only defined when HOTPLUG_CPU is enabled? On
> arm64 we can end up with this option disabled if SUSPEND is disabled.

Yep, only with HOTPLUG_CPU.  And yes, both SUSPEND and HIBERNATION can
force HOTPLUG_CPU, so if you have neiter SUSPEND nor HIBERNATION, you
won't have HOTPLUG_CPU.  This -should- be OK, because you should also
not have __cpu_die() if !HOTPLUG_CPU.

Or am I missing your point?

							Thanx, Paul

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