linux-kernel - [RFC PATCH 04/10] S390: smp: remove call to ipi_call_lock()/ipi_call

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Date:	Tue, 29 May 2012 15:15:59 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	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,
	srivatsa.bhat@...ux.vnet.ibm.com,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux390@...ibm.com, linux-s390@...r.kernel.org
Subject: [RFC PATCH 04/10] S390: smp: remove call to ipi_call_lock()/ipi_call_unlock()

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: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: linux390@...ibm.com
Cc: linux-s390@...r.kernel.org
---
 arch/s390/kernel/smp.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 647ba94..14c8a08 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -716,9 +716,7 @@ static void __cpuinit smp_start_secondary(void *cpuvoid)
 	init_cpu_vtimer();
 	pfault_init();
 	notify_cpu_starting(smp_processor_id());
-	ipi_call_lock();
 	set_cpu_online(smp_processor_id(), true);
-	ipi_call_unlock();
 	local_irq_enable();
 	/* cpu_idle will call schedule for us */
 	cpu_idle();
-- 
1.7.5.4

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