linux-kernel - [tip:x86/apic] x86, smpboot: Remove pointless preempt_disable() in native_smp_prepare

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Date:	Fri, 5 Dec 2014 15:25:33 -0800
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	mingo@...nel.org, joro@...tes.org, hpa@...or.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	jiang.liu@...ux.intel.com, bp@...en8.de
Subject: [tip:x86/apic] x86, smpboot: Remove pointless preempt_disable()
  in native_smp_prepare_cpus()

Commit-ID:  dd60143c04f257bace7c8d805eb1f4aec461b138
Gitweb:     http://git.kernel.org/tip/dd60143c04f257bace7c8d805eb1f4aec461b138
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Fri, 5 Dec 2014 08:48:29 +0000
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sat, 6 Dec 2014 00:19:25 +0100

x86, smpboot: Remove pointless preempt_disable() in native_smp_prepare_cpus()

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>
---
 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 4d2128a..2dc789d 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)
--
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