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Subject[patch 1/5] 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>
---
arch/x86/kernel/smpboot.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)

Index: tip/arch/x86/kernel/smpboot.c
===================================================================
--- tip.orig/arch/x86/kernel/smpboot.c
+++ tip/arch/x86/kernel/smpboot.c
@@ -1084,7 +1084,6 @@ void __init native_smp_prepare_cpus(unsi
{
unsigned int i;

- preempt_disable();
smp_cpu_index_default();

/*
@@ -1102,22 +1101,19 @@ void __init native_smp_prepare_cpus(unsi
}
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(unsi
uv_system_init();

set_mtrr_aps_delayed_init();
-out:
- preempt_enable();
}

void arch_enable_nonboot_cpus_begin(void)



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