linux-kernel - Re: [PATCH 08/10] SPARC: smp: remove call to ipi_call_lock_irq()/ipi_call_unlock

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Date:	Tue, 29 May 2012 04:14:58 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	srivatsa.bhat@...ux.vnet.ibm.com
Cc:	yong.zhang0@...il.com, linux-kernel@...r.kernel.org,
	ralf@...ux-mips.org, sshtylyov@...sta.com, david.daney@...ium.com,
	nikunj@...ux.vnet.ibm.com, paulmck@...ux.vnet.ibm.com,
	axboe@...nel.dk, mingo@...nel.org, tglx@...utronix.de,
	peterz@...radead.org, akpm@...ux-foundation.org,
	sparclinux@...r.kernel.org
Subject: Re: [PATCH 08/10] SPARC: smp: remove call to
 ipi_call_lock_irq()/ipi_call_unlock_irq()

From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Date: Tue, 29 May 2012 13:31:54 +0530

> On 05/29/2012 12:46 PM, 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.
>> 
>> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
>> Cc: "David S. Miller" <davem@...emloft.net>
>> Cc: sparclinux@...r.kernel.org
>> ---
>>  arch/sparc/kernel/smp_64.c |    6 ++----
>>  1 files changed, 2 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
>> index f591598..60e745c 100644
>> --- a/arch/sparc/kernel/smp_64.c
>> +++ b/arch/sparc/kernel/smp_64.c
>> @@ -124,9 +124,9 @@ void __cpuinit smp_callin(void)
>>  	while (!cpumask_test_cpu(cpuid, &smp_commenced_mask))
>>  		rmb();
>> 
>> -	ipi_call_lock_irq();
>> +	local_irq_disable();
> 
> 
> This looks odd. IRQs must not have been enabled at this point.
> Just remove the call to local_irq_enable() that is found a few lines above
> this line and then you won't have to add this call to local_irq_disable().

Agreed.
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