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    Subject[tip:x86/apic-cleanups] x86: apic: Cleanup and simplify setup_local_APIC()
    Commit-ID:  0aa002fe602939370e9476e5ec32b562000a0425
    Gitweb: http://git.kernel.org/tip/0aa002fe602939370e9476e5ec32b562000a0425
    Author: Tejun Heo <tj@kernel.org>
    AuthorDate: Thu, 9 Dec 2010 11:47:21 +0100
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 10 Dec 2010 13:46:26 +0100

    x86: apic: Cleanup and simplify setup_local_APIC()

    setup_local_APIC() is used to setup local APIC early during CPU
    initialization and already assumes that preemption is disabled on
    entry. However, The function unnecessarily disables and enables
    preemption and uses smp_processor_id() multiple times in and out of
    the nested preemption disabled section. This gives the wrong
    impression that the function might be able to handle being called with
    preemption enabled and/or migrated to another processor in the middle.

    Make it clear that the function is always called with preemption
    disabled, drop the confusing preemption disable block and call
    smp_processor_id() once at the beginning of the function.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>
    Reviewed-by: Pekka Enberg <penberg@kernel.org>
    Cc: Yinghai Lu <yinghai@kernel.org>
    Cc: brgerst@gmail.com
    LKML-Reference: <4D00B3B9.7060702@kernel.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    arch/x86/kernel/apic/apic.c | 21 +++++++++------------
    1 files changed, 9 insertions(+), 12 deletions(-)

    diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
    index 8933936..c0f6426 100644
    --- a/arch/x86/kernel/apic/apic.c
    +++ b/arch/x86/kernel/apic/apic.c
    @@ -1195,12 +1195,15 @@ static void __cpuinit lapic_setup_esr(void)
    oldvalue, value);
    }

    -
    /**
    * setup_local_APIC - setup the local APIC
    + *
    + * Used to setup local APIC while initializing BSP or bringin up APs.
    + * Always called with preemption disabled.
    */
    void __cpuinit setup_local_APIC(void)
    {
    + int cpu = smp_processor_id();
    unsigned int value, queued;
    int i, j, acked = 0;
    unsigned long long tsc = 0, ntsc;
    @@ -1225,8 +1228,6 @@ void __cpuinit setup_local_APIC(void)
    #endif
    perf_events_lapic_init();

    - preempt_disable();
    -
    /*
    * Double-check whether this APIC is really registered.
    * This is meaningless in clustered apic mode, so we skip it.
    @@ -1342,21 +1343,19 @@ void __cpuinit setup_local_APIC(void)
    * TODO: set up through-local-APIC from through-I/O-APIC? --macro
    */
    value = apic_read(APIC_LVT0) & APIC_LVT_MASKED;
    - if (!smp_processor_id() && (pic_mode || !value)) {
    + if (!cpu && (pic_mode || !value)) {
    value = APIC_DM_EXTINT;
    - apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n",
    - smp_processor_id());
    + apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n", cpu);
    } else {
    value = APIC_DM_EXTINT | APIC_LVT_MASKED;
    - apic_printk(APIC_VERBOSE, "masked ExtINT on CPU#%d\n",
    - smp_processor_id());
    + apic_printk(APIC_VERBOSE, "masked ExtINT on CPU#%d\n", cpu);
    }
    apic_write(APIC_LVT0, value);

    /*
    * only the BP should see the LINT1 NMI signal, obviously.
    */
    - if (!smp_processor_id())
    + if (!cpu)
    value = APIC_DM_NMI;
    else
    value = APIC_DM_NMI | APIC_LVT_MASKED;
    @@ -1364,11 +1363,9 @@ void __cpuinit setup_local_APIC(void)
    value |= APIC_LVT_LEVEL_TRIGGER;
    apic_write(APIC_LVT1, value);

    - preempt_enable();
    -
    #ifdef CONFIG_X86_MCE_INTEL
    /* Recheck CMCI information after local APIC is up on CPU #0 */
    - if (smp_processor_id() == 0)
    + if (!cpu)
    cmci_recheck();
    #endif
    }

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