Hello,

FYI this happens in mainline kernel 4.17.0-rc1.
It at least dates back to v4.16 .

It occurs in 2 out of 6 boots.

[    0.000000] Built 1 zonelists, mobility grouping on.  Total pages: 128869
[    0.000000] Kernel command line: ip=::::vm-intel12-yocto-x86_64-2::dhcp root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-intel12-yocto-x86_64-2/boot-1-yocto-minimal-x86_64-2016-04-22.cgz-60cc43fc888428bb2f18f08997432d426a243338-20180418-63270-jrkd3n-1.yaml ARCH=x86_64 kconfig=x86_64-randconfig-s0-04090505 branch=linux-devel/devel-spot-201804082042 commit=60cc43fc888428bb2f18f08997432d426a243338 BOOT_IMAGE=/pkg/linux/x86_64-randconfig-s0-04090505/gcc-6/60cc43fc888428bb2f18f08997432d426a243338/vmlinuz-4.17.0-rc1 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-intel12-yocto-x86_64/yocto-minimal-x86_64-2016-04-22.cgz/x86_64-randconfig-s0-04090505/gcc-6/60cc43fc888428bb2f18f08997432d426a243338/2 LKP_SERVER=inn debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 co
[    0.000000] sysrq: sysrq always enabled.
[    0.000000] Dentry cache hash table entries: 65536 (order: 7, 524288 bytes)
[    0.000000] Inode-cache hash table entries: 32768 (order: 6, 262144 bytes)
[    0.000000] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[    0.000000] PGD 0 P4D 0
[    0.000000] Oops: 0000 [#1] PREEMPT DEBUG_PAGEALLOC
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.17.0-rc1 #1
[    0.000000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
[    0.000000] RIP: 0010:per_cpu_ptr_to_phys+0xf1/0x14e:
						__section_mem_map_addr at include/linux/mmzone.h:1188
						 (inlined by) per_cpu_ptr_to_phys at mm/percpu.c:1849
[    0.000000] RSP: 0000:ffffffff87803ea0 EFLAGS: 00010046
[    0.000000] RAX: ffff88001f00c240 RBX: ffffffff87809000 RCX: 0000000000000000
[    0.000000] RDX: ffffffffffffffff RSI: ffff88001ffd2000 RDI: 0000000000000000
[    0.000000] RBP: ffffffff87803ea8 R08: 0000000000000000 R09: ffff88001f8c4000
[    0.000000] R10: 000000000000b080 R11: ffffffff8868746c R12: 8000000000000161
[    0.000000] R13: ffffffff87a70940 R14: ffffffff87a772e0 R15: 0000000000000000
[    0.000000] FS:  0000000000000000(0000) GS:ffffffff8783d000(0000) knlGS:0000000000000000
[    0.000000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.000000] CR2: 0000000000000000 CR3: 000000001c21a000 CR4: 00000000000006b0
[    0.000000] Call Trace:
[    0.000000]  setup_cpu_entry_areas+0x35/0x15e:
						setup_cpu_entry_area at arch/x86/mm/cpu_entry_area.c:104
						 (inlined by) setup_cpu_entry_areas at arch/x86/mm/cpu_entry_area.c:177
[    0.000000]  trap_init+0x9/0x6e:
						trap_init at arch/x86/kernel/traps.c:949
[    0.000000]  start_kernel+0x241/0x54b:
						mm_init at init/main.c:519
						 (inlined by) start_kernel at init/main.c:589
[    0.000000]  x86_64_start_reservations+0x2a/0x2c:
						x86_64_start_reservations at arch/x86/kernel/head64.c:446
[    0.000000]  x86_64_start_kernel+0x76/0x79:
						x86_64_start_kernel at arch/x86/kernel/head64.c:427
[    0.000000]  secondary_startup_64+0xa5/0xb0:
						secondary_startup_64 at arch/x86/kernel/head_64.S:242
[    0.000000] Code: c1 e1 05 48 01 ca 48 8b 12 eb 23 48 8b 10 48 89 d1 48 c1 e9 34 48 8b 0c ce 48 85 c9 74 0d 48 c1 ea 28 81 e2 e0 0f 00 00 48 01 d1 <48> 8b 11 48 83 e2 f8 81 e3 ff 0f 00 00 48 29 d0 48 c1 f8 06 48
[    0.000000] RIP: per_cpu_ptr_to_phys+0xf1/0x14e:
						__section_mem_map_addr at include/linux/mmzone.h:1188
						 (inlined by) per_cpu_ptr_to_phys at mm/percpu.c:1849 RSP: ffffffff87803ea0
[    0.000000] CR2: 0000000000000000
[    0.000000] ---[ end trace 142a0423c71f6258 ]---
[    0.000000] Kernel panic - not syncing: Fatal exception

Attached the full dmesg, kconfig and reproduce scripts.

Thanks,
Fengguang