linux-kernel - [Patch v1 01/17] x86, smpboot: Remove pointless preempt_disable() in native_smp_prepare

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Date:	Wed, 17 Dec 2014 12:35:32 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Joerg Roedel <joro@...tes.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>, x86@...nel.org,
	Toshi Kani <toshi.kani@...com>,
	Igor Mammedov <imammedo@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Lan Tianyu <tianyu.lan@...el.com>
Cc:	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [Patch v1 01/17] x86, smpboot: Remove pointless preempt_disable() in native_smp_prepare_cpus()

From: Thomas Gleixner <tglx@...utronix.de>

There is no reason to keep preemption disabled in this function.

We only have two other threads live: kthreadd and idle. Neither of
them is going to preempt. But that preempt_disable forces all the code
inside to do GFP_ATOMIC allocations which is just insane.

Remove it.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Borislav Petkov <bp@...en8.de>
Cc: Jiang Liu <jiang.liu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>
Cc: x86@...nel.org
Link: http://lkml.kernel.org/r/20141205084147.153643952@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
---
 arch/x86/kernel/smpboot.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 7a8f5845e8eb..6d7022c683e3 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1084,7 +1084,6 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 {
 	unsigned int i;
 
-	preempt_disable();
 	smp_cpu_index_default();
 
 	/*
@@ -1102,22 +1101,19 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	}
 	set_cpu_sibling_map(0);
 
-
 	if (smp_sanity_check(max_cpus) < 0) {
 		pr_info("SMP disabled\n");
 		disable_smp();
-		goto out;
+		return;
 	}
 
 	default_setup_apic_routing();
 
-	preempt_disable();
 	if (read_apic_id() != boot_cpu_physical_apicid) {
 		panic("Boot APIC ID in local APIC unexpected (%d vs %d)",
 		     read_apic_id(), boot_cpu_physical_apicid);
 		/* Or can we switch back to PIC here? */
 	}
-	preempt_enable();
 
 	connect_bsp_APIC();
 
@@ -1151,8 +1147,6 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 		uv_system_init();
 
 	set_mtrr_aps_delayed_init();
-out:
-	preempt_enable();
 }
 
 void arch_enable_nonboot_cpus_begin(void)
-- 
1.7.10.4

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