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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@linutronix.de>
AuthorDate: Fri, 5 Dec 2014 08:48:29 +0000
Committer: Thomas Gleixner <tglx@linutronix.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@linutronix.de>
Tested-by: Borislav Petkov <bp@alien8.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20141205084147.153643952@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.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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