Comment 2 for bug 1649821

FWIW, here is the full boot log (it crashes very early):
[ 0.014281] Freeing SMP alternatives memory: 28K (ffffffff820b2000 - ffffffff820b9000)
[ 0.021560] ftrace: allocating 31878 entries in 125 pages
[ 0.248098] smpboot: Max logical packages: 15
[ 0.248123] smpboot: APIC(0) Converting physical 0 to logical package 0
[ 0.248140] smpboot: APIC(2) Converting physical 2 to logical package 1
[ 0.248671] x2apic: IRQ remapping doesn't support X2APIC mode
[ 0.249178] Switched APIC routing to physical flat.
[ 0.251027] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=0 pin2=0
[ 0.296235] clocksource: xen: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[ 0.296440] installing Xen timer for CPU 0
[ 0.296824] smpboot: CPU0: Intel(R) Xeon(R) CPU X3430 @ 2.40GHz (family: 0x6, model: 0x1e, stepping: 0x5)
[ 0.296897] cpu 0 spinlock event irq 53
[ 0.296916] Performance Events: unsupported p6 CPU model 30 no PMU driver, software events only.
[ 0.297819] NMI watchdog: disabled (cpu0): hardware events not enabled
[ 0.297841] NMI watchdog: Shutting down hard lockup detector on all cpus
[ 0.297919] installing Xen timer for CPU 1
[ 0.297997] x86: Booting SMP configuration:
[ 0.298010] .... node #0, CPUs: #1
[ 0.008000] calibrate_delay_direct() dropping max bogoMips estimate 3 = 11283848
[ 0.384000] ------------[ cut here ]------------
[ 0.384000] kernel BUG at /build/linux-Ay7j_C/linux-4.4.0/drivers/xen/events/events_base.c:1210!
[ 0.384000] invalid opcode: 0000 [#1] SMP
[ 0.384000] Modules linked in:
[ 0.384000] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-21-generic #37-Ubuntu
[ 0.384000] Hardware name: Xen HVM domU, BIOS 4.6.1-xs124820 04/20/2016
[ 0.384000] task: ffff88003d758000 ti: ffff88003d760000 task.ti: ffff88003d760000
[ 0.384000] RIP: 0010:[<ffffffff814c97c9>] [<ffffffff814c97c9>] xen_send_IPI_one+0x59/0x60
[ 0.384000] RSP: 0000:ffff88003d763d30 EFLAGS: 00010086
[ 0.384000] RAX: ffff88003da522fc RBX: 00000005528d31c0 RCX: 0000000000000001
[ 0.384000] RDX: ffff88003da57840 RSI: 0000000000000003 RDI: 00000000ffffffff
[ 0.384000] RBP: ffff88003d763d30 R08: 0000000000000100 R09: ffff88003f7c7900
[ 0.384000] R10: ffff88003da4a080 R11: ffff88003da4a060 R12: 000000000000a90d
[ 0.384000] R13: 000000055285a88a R14: 0000000000000001 R15: ffffffff820d3db0
[ 0.384000] FS: 0000000000000000(0000) GS:ffff88003da00000(0000) knlGS:0000000000000000
[ 0.384000] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 0.384000] CR2: ffff880002200000 CR3: 0000000001e0a000 CR4: 00000000000006f0
[ 0.384000] Stack:
[ 0.384000] ffff88003d763d40 ffffffff8102be9e ffff88003d763de0 ffffffff810cabc2
[ 0.384000] ffffffff810ca6d1 ffff88003da4a060 ffff88003da4a080 0000000000000001
[ 0.384000] ffff88003da4a080 ffffffff820d3db0 0000000000080000 0000000500000000
[ 0.384000] Call Trace:
[ 0.384000] [<ffffffff8102be9e>] xen_qlock_kick+0xe/0x10
[ 0.384000] [<ffffffff810cabc2>] __pv_queued_spin_unlock+0xb2/0xf0
[ 0.384000] [<ffffffff810ca6d1>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
[ 0.384000] [<ffffffff81052936>] ? check_tsc_warp+0x76/0x150
[ 0.384000] [<ffffffff81052aa6>] check_tsc_sync_source+0x96/0x160
[ 0.384000] [<ffffffff81051e28>] native_cpu_up+0x3d8/0x9f0
[ 0.384000] [<ffffffff8102b315>] xen_hvm_cpu_up+0x35/0x80
[ 0.384000] [<ffffffff8108198c>] _cpu_up+0x13c/0x180
[ 0.384000] [<ffffffff81081a4a>] cpu_up+0x7a/0xa0
[ 0.384000] [<ffffffff81f80dfc>] smp_init+0x7f/0x81
[ 0.384000] [<ffffffff81f5a121>] kernel_init_freeable+0xef/0x212
[ 0.384000] [<ffffffff81817f30>] ? rest_init+0x80/0x80
[ 0.384000] [<ffffffff81817f3e>] kernel_init+0xe/0xe0
[ 0.384000] [<ffffffff8182488f>] ret_from_fork+0x3f/0x70
[ 0.384000] [<ffffffff81817f30>] ? rest_init+0x80/0x80
[ 0.384000] Code: 8e e9 ff ff 5d c3 bf 0b 00 00 00 48 63 f1 31 d2 e8 4d 7b b3 ff 85 c0 79 eb 89 c2 89 ce 48 c7 c7 58 71 d2 81 e8 f0 24 cc ff 5d c3 <0f> 0b 0f 1f 44 00 00 66 66 66 66 90 55 48 89 e5 53 65 48 8b 1d
[ 0.384000] RIP [<ffffffff814c97c9>] xen_send_IPI_one+0x59/0x60
[ 0.384000] RSP <ffff88003d763d30>
[ 0.384000] ---[ end trace d1d38124e72edb7a ]---
[ 0.384015] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
[ 0.384015]