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>

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 7a8f5845e8eb9140e849b52cabf852a82313e979..6d7022c683e31555967f20edfc18b490576bc10b 100644 (file)
--- 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)