This panic is unrelated to circular lock issue that I reported in a separate thread, that also happens during memory hotremove. xakep ~/x/linux$ git describe v5.1-12317-ga6a4b66bd8f4 Config is attached, qemu script is following: qemu-system-x86_64 \ -enable-kvm \ -cpu host \ -parallel none \ -echr 1 \ -serial none \ -chardev stdio,id=console,signal=off,mux=on \ -serial chardev:console \ -mon chardev=console \ -vga none \ -display none \ -kernel pmem/native/arch/x86/boot/bzImage \ -m 8G,slots=1,maxmem=16G \ -smp 8 \ -fsdev local,id=virtfs1,path=/,security_model=none \ -device virtio-9p-pci,fsdev=virtfs1,mount_tag=hostfs \ -append 'earlyprintk=serial,ttyS0,115200 console=ttyS0 TERM=xterm ip=dhcp memmap=2G!6G loglevel=7' The unusual case with this script is that 2G reserved for pmem device: memmap=2G!6G. Otherwise, it is a normal layout. Unfortunately, it does not happen every time, but I have hit it a couple times. # QEMU 4.0.0 monitor - type 'help' for more information (qemu) object_add memory-backend-ram,id=mem1,size=1G (qemu) device_add pc-dimm,id=dimm1,memdev=mem1 # echo online_movable > /sys/devices/system/memory/memory79/state [ 40.219090] Built 1 zonelists, mobility grouping on. Total pages: 1529279 [ 40.223258] Policy zone: Normal # (qemu) device_del dimm1 (qemu) [ 49.624600] Offlined Pages 32768 [ 49.625796] Built 1 zonelists, mobility grouping on. Total pages: 1516352 [ 49.627841] Policy zone: Normal [ 49.630932] BUG: kernel NULL pointer dereference, address: 0000000000000698 [ 49.633704] #PF: supervisor read access in kernel mode [ 49.635689] #PF: error_code(0x0000) - not-present page [ 49.637620] PGD 8000000236b59067 P4D 8000000236b59067 PUD 2358fe067 PMD 0 [ 49.640163] Oops: 0000 [#1] SMP PTI [ 49.641223] CPU: 0 PID: 7 Comm: kworker/u16:0 Not tainted 5.1.0_pt_pmem #38 [ 49.643183] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014 [ 49.645858] Workqueue: kacpi_hotplug acpi_hotplug_work_fn [ 49.647101] RIP: 0010:__remove_pages+0x1a/0x460 [ 49.648165] Code: e9 bb a9 fd ff 0f 0b 66 0f 1f 84 00 00 00 00 00 41 57 48 89 f8 49 89 ff 41 56 49 89 f6 41 55 41 54 55 53 48 89 d3 48 83 ec 50 <48> 2b 47 58 48 89 4c 24 48 48 3d 00 19 00 00 75 09 48 85 c9 0f 85 [ 49.651925] RSP: 0018:ffffbd1000c8fcb8 EFLAGS: 00010286 [ 49.652857] RAX: 0000000000000640 RBX: 0000000000040000 RCX: 0000000000000000 [ 49.654139] RDX: 0000000000040000 RSI: 0000000000240000 RDI: 0000000000000640 [ 49.655393] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000040000000 [ 49.656523] R10: 0000000040000000 R11: 0000000240000000 R12: 0000000040000000 [ 49.657654] R13: 0000000240000000 R14: 0000000000240000 R15: 0000000000000640 [ 49.658828] FS: 0000000000000000(0000) GS:ffff9b4bf9800000(0000) knlGS:0000000000000000 [ 49.660178] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 49.661033] CR2: 0000000000000698 CR3: 00000002382e0006 CR4: 0000000000360ef0 [ 49.662114] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 49.663172] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 49.664243] Call Trace: [ 49.664622] ? memblock_isolate_range+0xc4/0x139 [ 49.665290] ? firmware_map_add_hotplug+0x7e/0xde [ 49.665908] ? memblock_remove_region+0x30/0x74 [ 49.666498] arch_remove_memory+0x6f/0xa0 [ 49.667012] __remove_memory+0xab/0x130 [ 49.667492] ? walk_memory_range+0xa1/0xe0 [ 49.668008] acpi_memory_device_remove+0x67/0xe0 [ 49.668595] acpi_bus_trim+0x50/0x90 [ 49.669051] acpi_device_hotplug+0x2fa/0x3e0 [ 49.669590] acpi_hotplug_work_fn+0x15/0x20 [ 49.670116] process_one_work+0x2a0/0x650 [ 49.670577] worker_thread+0x34/0x3d0 [ 49.670997] ? process_one_work+0x650/0x650 [ 49.671503] kthread+0x118/0x130 [ 49.671879] ? kthread_create_on_node+0x60/0x60 [ 49.672411] ret_from_fork+0x3a/0x50 [ 49.672836] Modules linked in: [ 49.673190] CR2: 0000000000000698 [ 49.673583] ---[ end trace 6b727d3a8ce48aa1 ]--- [ 49.674120] RIP: 0010:__remove_pages+0x1a/0x460 [ 49.674624] Code: e9 bb a9 fd ff 0f 0b 66 0f 1f 84 00 00 00 00 00 41 57 48 89 f8 49 89 ff 41 56 49 89 f6 41 55 41 54 55 53 48 89 d3 48 83 ec 50 <48> 2b 47 58 48 89 4c 24 48 48 3d 00 19 00 00 75 09 48 85 c9 0f 85 [ 49.676600] RSP: 0018:ffffbd1000c8fcb8 EFLAGS: 00010286 [ 49.677159] RAX: 0000000000000640 RBX: 0000000000040000 RCX: 0000000000000000 [ 49.677960] RDX: 0000000000040000 RSI: 0000000000240000 RDI: 0000000000000640 [ 49.678813] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000040000000 [ 49.679633] R10: 0000000040000000 R11: 0000000240000000 R12: 0000000040000000 [ 49.680455] R13: 0000000240000000 R14: 0000000000240000 R15: 0000000000000640 [ 49.681243] FS: 0000000000000000(0000) GS:ffff9b4bf9800000(0000) knlGS:0000000000000000 [ 49.682168] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 49.682813] CR2: 0000000000000698 CR3: 00000002382e0006 CR4: 0000000000360ef0 [ 49.683573] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 49.684239] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 49.684901] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:34 [ 49.685690] in_atomic(): 0, irqs_disabled(): 1, pid: 7, name: kworker/u16:0 [ 49.686314] INFO: lockdep is turned off. [ 49.686684] irq event stamp: 22546 [ 49.687003] hardirqs last enabled at (22545): [] kfree+0xba/0x230 [ 49.687692] hardirqs last disabled at (22546): [] trace_hardirqs_off_thunk+0x1a/0x1c [ 49.688561] softirqs last enabled at (22526): [] __do_softirq+0x33e/0x455 [ 49.689348] softirqs last disabled at (22519): [] irq_exit+0xb6/0xc0 [ 49.690088] CPU: 0 PID: 7 Comm: kworker/u16:0 Tainted: G D 5.1.0_pt_pmem #38 [ 49.690811] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014 [ 49.691704] Workqueue: kacpi_hotplug acpi_hotplug_work_fn [ 49.692185] Call Trace: [ 49.692398] dump_stack+0x67/0x90 [ 49.692690] ___might_sleep.cold.87+0x9f/0xaf [ 49.693099] exit_signals+0x2b/0x240 [ 49.693453] do_exit+0xab/0xc10 [ 49.693770] ? process_one_work+0x650/0x650 [ 49.694160] ? kthread+0x118/0x130 [ 49.694487] rewind_stack_do_exit+0x17/0x20 [ 77.418619] random: fast init done