x86, smpboot: Remove pointless preempt_disable() in native_smp_prepar…

…e_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 <[email protected]>
Tested-by: Borislav Petkov <[email protected]>
Cc: Jiang Liu <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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)