Hi guys, while testing memhotplug, I spotted the following trace: ===== linux kernel: WARNING: CPU: 0 PID: 64 at ./include/linux/gfp.h:467 vmemmap_alloc_block+0x4e/0xc9 linux kernel: Modules linked in: fuse(E) nf_log_ipv6(E) nf_log_ipv4(E) nf_log_common(E) xt_LOG(E) xt_limit(E) xt_pkttype(E) iscsi_ibft(E) iscsi_boot_sysfs(E) ip6t_REJECT(E) xt_tcpudp(E) nf_conntrack_ipv6(E) nf_defrag_ipv6(E) ip6table_raw(E) ipt_REJECT(E) iptable_raw(E) xt_CT(E) iptable_filter(E) ip6table_mangle(E) nf_conntrack_netbios_ns(E) nf_conntrack_broadcast(E) nf_conntrack_ipv4(E) nf_defrag_ipv4(E) ip_tables(E) xt_conntrack(E) nf_conntrack(E) ip6table_filter(E) ip6_tables(E) x_tables(E) bochs_drm(E) ttm(E) drm_kms_helper(E) drm(E) syscopyarea(E) sysfillrect(E) sysimgblt(E) fb_sys_fops(E) pcspkr(E) ppdev(E) i2c_piix4(E) joydev(E) parport_pc(E) parport(E) btrfs(E) libcrc32c(E) xor(E) zstd_decompress(E) zstd_compress(E) xxhash(E) raid6_pq(E) sr_mod(E) cdrom(E) sd_mod(E) ata_generic(E) ata_piix(E) linux kernel: ahci(E) libahci(E) floppy(E) serio_raw(E) libata(E) button(E) sg(E) dm_multipath(E) dm_mod(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) scsi_mod(E) autofs4(E) linux kernel: CPU: 0 PID: 64 Comm: kworker/u4:1 Tainted: G W E 4.17.0-rc5-next-20180517-1-default+ #66 linux kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014 linux kernel: Workqueue: kacpi_hotplug acpi_hotplug_work_fn linux kernel: RIP: 0010:vmemmap_alloc_block+0x4e/0xc9 linux kernel: Code: fb ff 8d 69 01 75 07 65 8b 1d 9d cb 93 7e 81 fb ff 03 00 00 76 02 0f 0b 48 63 c3 48 0f a3 05 c8 b1 b4 00 0f 92 c0 84 c0 75 02 <0f> 0b 31 c9 89 da 89 ee bf c0 06 40 01 e8 0f d1 ad ff 48 85 c0 74 linux kernel: RSP: 0018:ffffc90000d03bf0 EFLAGS: 00010246 linux kernel: RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000008 linux kernel: RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00000000000001ff linux kernel: RBP: 0000000000000009 R08: 0000000000000001 R09: ffffc90000d03ae8 linux kernel: R10: 0000000000000001 R11: 0000000000000000 R12: ffffea0006000000 linux kernel: R13: ffffea0005e00000 R14: ffffea0006000000 R15: 0000000000000001 linux kernel: FS: 0000000000000000(0000) GS:ffff88013fc00000(0000) knlGS:0000000000000000 linux kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 linux kernel: CR2: 00007fa92a698018 CR3: 00000001184ce000 CR4: 00000000000006f0 linux kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 linux kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 linux kernel: Call Trace: linux kernel: vmemmap_populate+0xf2/0x2ae linux kernel: sparse_mem_map_populate+0x28/0x35 linux kernel: sparse_add_one_section+0x4c/0x187 linux kernel: __add_pages+0xe7/0x1a0 linux kernel: add_pages+0x16/0x70 linux kernel: add_memory_resource+0xa3/0x1d0 linux kernel: add_memory+0xe4/0x110 linux kernel: acpi_memory_device_add+0x134/0x2e0 linux kernel: acpi_bus_attach+0xd9/0x190 linux kernel: acpi_bus_scan+0x37/0x70 linux kernel: acpi_device_hotplug+0x389/0x4e0 linux kernel: acpi_hotplug_work_fn+0x1a/0x30 linux kernel: process_one_work+0x146/0x340 linux kernel: worker_thread+0x47/0x3e0 linux kernel: kthread+0xf5/0x130 linux kernel: ? max_active_store+0x60/0x60 linux kernel: ? kthread_bind+0x10/0x10 linux kernel: ret_from_fork+0x35/0x40 linux kernel: ---[ end trace 2e2241f4e2f2f018 ]--- ==== This happens when adding memory to a node that is currently offline. add_memory_resource() { ... new_node = !node_online(nid); if (new_node) { pgdat = hotadd_new_pgdat(nid, start); ret = -ENOMEM; if (!pgdat) goto error; } ret = arch_add_memory(nid, start, size, NULL, true); node_set_online(nid); ... } arch_add_memory() ends up in vmemmap_populate()->vmemmap_alloc_block_buf()->vmemmap_alloc_block() vmemmap_alloc_block() calls alloc_pages_node()->__alloc_pages_node(). In __alloc_pages_node(), we have a check to see if the node where we are requesting memory is onlined. static inline struct page * __alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order) { VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); VM_WARN_ON(!node_online(nid)); ... } But it is not, since we online the node after the call to arch_add_memory(). After thinking a while, I thought about 3 ways to go: 1) In case the memory is offlined, after allocating it, we can set some of its field to a "magic" value. Something like: pgdat->node_present_pages = (-1UL) or pgdat->nr_zones = -1 And later on, in __alloc_pages_node(), we can check for the magic value, and if it is set we do not check for VM_WARN_ON(!node_online(nid)) 2) Move node_set_online() above arch_add_memory. Although I think we cannot really do that. I guess we could collide with someone seeing that we are online, when we are not 100%. 3) Live with it? Any ideas? Thanks Oscar Salvador