CPU interrupts need to be disabled on a cpu being taken down.
When a cpu is hot-plugged out of the system the following sequence occurs.

On the CPU where the hotplug sequence was initiated:
    cpu_down
        _cpu_down {
            __cpu_notify(CPU_DOWN_PREPARE
            __stop_machine(take_cpu_down
                wait for cpu to run disable code.
            __cpu_die
        }

On the CPU  being disabled:
    take_cpu_down
        __cpu_disable {
            mp_ops->cpu_disable
                bmips_cpu_disable
                    clear_c0_status(IE_IRQ5) (added)
            cpu_notify(CPU_DYING...
        }

Before the cpu_notifier is called with CPU_DYING, all interrupts on the
dying cpu must be disabled.  This guarantees that before tick_notify is
called with the CPU_DYING event and sets the clock device pointer to
NULL, there can not be any more clock interrupts.

When this wasn't done, an unfortunately-timed timer interrupt sometimes
caused hangs immediately prior to system suspend:

    Debug PM is not enabled. To enable partial suspend, rebuild kernel with CONFIG_PM_DEBUG
    Pass 1 out of 1,PM: Syncing filesystems ... mode=none, tp1=done.
    1, flags=5, cycle_tp=, sleep=
    Freezing user space processes ... (elapsed 0.01 seconds) done.
    Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
    PM: suspend of devices complete after 54.199 msecs
    PM: late suspend of devices complete after 0.172 msecs
    Disabling non-boot CPUs ...
    SMP: CPU1 is offline
    INFO: rcu_sched detected stalls on CPUs/tasks: { 3} (detected by 0, t=62537 jiffies)
    Call Trace:
    [<804baa78>] dump_stack+0x8/0x34
    [<8008a2d8>] __rcu_pending+0x4b8/0x55c
    [<8008adf4>] rcu_check_callbacks+0x78/0x180
    [<80037830>] update_process_times+0x40/0x6c
    [<80072fe4>] tick_sched_timer+0x74/0xe4
    [<80050180>] __run_hrtimer.clone.30+0x64/0x140
    [<80051150>] hrtimer_interrupt+0x19c/0x4bc
    [<8000cdb8>] c0_compare_interrupt+0x50/0x88
    [<80081b18>] handle_irq_event_percpu+0x5c/0x2f4
    [<80086490>] handle_percpu_irq+0x8c/0xc0
    [<800811b4>] generic_handle_irq+0x34/0x54
    [<800067dc>] do_IRQ+0x18/0x2c
    [<8000375c>] plat_irq_dispatch+0xd0/0x128
    [<80004a04>] ret_from_irq+0x0/0x4
    [<80004c40>] r4k_wait+0x20/0x40
    [<80006b6c>] cpu_idle+0x98/0xf0
    [<805d3988>] start_kernel+0x424/0x440
Signed-off-by: Jon Fraser <jfraser@broadcom.com>
Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: f.fainelli@gmail.com
Cc: mbizon@freebox.fr
Cc: jogo@openwrt.org
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8160/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>