We have observed on few x86 machines with rtc-cmos device that
hpet_rtc_interrupt() is called just after irq registration and before
cmos_do_probe() could call hpet_rtc_timer_init().

So, neither hpet_default_delta nor hpet_t1_cmp is initialized by the time
interrupt is raised in the given situation, and this results in NMI
watchdog LOCKUP.

It has only been observed sporadically on kdump secondary kernels.

See the call trace:
---<-snip->---
[   27.913194] Kernel panic - not syncing: Watchdog detected hard LOCKUP on cpu 0
[   27.915371] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0-342.el7.x86_64 #1
[   27.917503] Hardware name: HP ProLiant DL160 Gen8, BIOS J03 02/10/2014
[   27.919455]  ffffffff8186a728 0000000059c82488 ffff880034e05af0 ffffffff81637bd4
[   27.921870]  ffff880034e05b70 ffffffff8163144a 0000000000000010 ffff880034e05b80
[   27.924257]  ffff880034e05b20 0000000059c82488 0000000000000000 0000000000000000
[   27.926599] Call Trace:
[   27.927352]  <NMI>  [<ffffffff81637bd4>] dump_stack+0x19/0x1b
[   27.929080]  [<ffffffff8163144a>] panic+0xd8/0x1e7
[   27.930588]  [<ffffffff8111d3e0>] ? restart_watchdog_hrtimer+0x50/0x50
[   27.932502]  [<ffffffff8111d4a2>] watchdog_overflow_callback+0xc2/0xd0
[   27.934427]  [<ffffffff811612c1>] __perf_event_overflow+0xa1/0x250
[   27.936232]  [<ffffffff81161d94>] perf_event_overflow+0x14/0x20
[   27.937957]  [<ffffffff81032ae8>] intel_pmu_handle_irq+0x1e8/0x470
[   27.939799]  [<ffffffff8164164b>] perf_event_nmi_handler+0x2b/0x50
[   27.941649]  [<ffffffff81640d99>] nmi_handle.isra.0+0x69/0xb0
[   27.943348]  [<ffffffff81640f49>] do_nmi+0x169/0x340
[   27.944802]  [<ffffffff816401d3>] end_repeat_nmi+0x1e/0x2e
[   27.946424]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.948197]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.949992]  [<ffffffff81056ee5>] ? hpet_rtc_interrupt+0x85/0x380
[   27.951816]  <<EOE>>  <IRQ>  [<ffffffff8108f5a3>] ? run_timer_softirq+0x43/0x340
[   27.954114]  [<ffffffff8111e24e>] handle_irq_event_percpu+0x3e/0x1e0
[   27.955962]  [<ffffffff8111e42d>] handle_irq_event+0x3d/0x60
[   27.957635]  [<ffffffff811210c7>] handle_edge_irq+0x77/0x130
[   27.959332]  [<ffffffff8101704f>] handle_irq+0xbf/0x150
[   27.960949]  [<ffffffff8164a86f>] do_IRQ+0x4f/0xf0
[   27.962434]  [<ffffffff8163faed>] common_interrupt+0x6d/0x6d
[   27.964101]  <EOI>  [<ffffffff8163f43b>] ? _raw_spin_unlock_irqrestore+0x1b/0x40
[   27.966308]  [<fffff8111ff07>] __setup_irq+0x2a7/0x570
[   28.067859]  [<ffffffff81056e60>] ? hpet_cpuhp_notify+0x140/0x140
[   28.069709]  [<ffffffff8112032c>] request_threaded_irq+0xcc/0x170
[   28.071585]  [<ffffffff814b24a6>] cmos_do_probe+0x1e6/0x450
[   28.073240]  [<ffffffff814b2710>] ? cmos_do_probe+0x450/0x450
[   28.074911]  [<ffffffff814b27cb>] cmos_pnp_probe+0xbb/0xc0
[   28.076533]  [<ffffffff8139b245>] pnp_device_probe+0x65/0xd0
[   28.078198]  [<ffffffff813f8ca7>] driver_probe_device+0x87/0x390
[   28.079971]  [<ffffffff813f9083>] __driver_attach+0x93/0xa0
[   28.081660]  [<ffffffff813f8ff0>] ? __device_attach+0x40/0x40
[   28.083662]  [<ffffffff813f6a13>] bus_for_each_dev+0x73/0xc0
[   28.085370]  [<ffffffff813f86fe>] driver_attach+0x1e/0x20
[   28.086974]  [<ffffffff813f8250>] bus_add_driver+0x200/0x2d0
[   28.088634]  [<ffffffff81ade49a>] ? rtc_sysfs_init+0xe/0xe
[   28.090349]  [<ffffffff813f9704>] driver_register+0x64/0xf0
[   28.091989]  [<ffffffff8139b070>] pnp_register_driver+0x20/0x30
[   28.093707]  [<ffffffff81ade4ab>] cmos_init+0x11/0x71
---<-snip->---

This patch moves hpet_rtc_timer_init() before IRQ registration, so that we
can gracefully handle such spurious interrupts. It also masks HPET RTC
interrupts, in case IRQ registration fails.

We were able to reproduce the problem in maximum 15 trials of kdump
secondary kernel boot on an hp-dl160gen8 FCoE host machine without this
patch.  However, more than 35 trials went fine after applying this patch.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Pratyush Anand <panand@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>