linux-kernel - Re: [RFC PATCH 09/10] POWERPC: smp: remove call to ipi_call_lock()/ipi_call

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Date:	Sat, 16 Jun 2012 09:32:19 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel@...r.kernel.org, ralf@...ux-mips.org,
	sshtylyov@...sta.com, david.daney@...ium.com,
	nikunj@...ux.vnet.ibm.com, axboe@...nel.dk, mingo@...nel.org,
	tglx@...utronix.de, peterz@...radead.org,
	akpm@...ux-foundation.org, srivatsa.bhat@...ux.vnet.ibm.com,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH 09/10] POWERPC: smp: remove call to
 ipi_call_lock()/ipi_call_unlock()

On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote:
> From: Yong Zhang <yong.zhang@...driver.com>
> 
> 1) call_function.lock used in smp_call_function_many() is just to protect
>    call_function.queue and &data->refs, cpu_online_mask is outside of the
>    lock. And it's not necessary to protect cpu_online_mask,
>    because data->cpumask is pre-calculate and even if a cpu is brougt up
>    when calling arch_send_call_function_ipi_mask(), it's harmless because
>    validation test in generic_smp_call_function_interrupt() will take care
>    of it.
> 
> 2) For cpu down issue, stop_machine() will guarantee that no concurrent
>    smp_call_fuction() is processing.

However, there is an effort to get rid of stop_machine() from the
CPU-down path...  So something else will be needed.

							Thanx, Paul

> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: linuxppc-dev@...ts.ozlabs.org
> ---
>  arch/powerpc/kernel/smp.c |    2 --
>  1 files changed, 0 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index e4cb343..e1417c4 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -571,7 +571,6 @@ void __devinit start_secondary(void *unused)
>  	if (system_state == SYSTEM_RUNNING)
>  		vdso_data->processorCount++;
>  #endif
> -	ipi_call_lock();
>  	notify_cpu_starting(cpu);
>  	set_cpu_online(cpu, true);
>  	/* Update sibling maps */
> @@ -601,7 +600,6 @@ void __devinit start_secondary(void *unused)
>  		of_node_put(np);
>  	}
>  	of_node_put(l2_cache);
> -	ipi_call_unlock();
> 
>  	local_irq_enable();
> 
> -- 
> 1.7.5.4
> 

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