No idea what caused this. System was under heavy load at the time and probably doing a reasonable amount of swapping. [35903.738172] page:000000000c20a49a refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x2b7d26 [35903.738176] flags: 0x2ffff0000000000() [35903.738180] raw: 02ffff0000000000 ffffe4265ef604c8 ffff9c9a1fbf2180 0000000000000000 [35903.738183] raw: 0000000000000001 0000000000000011 00000000ffffffff 0000000000000000 [35903.738184] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) [35903.738193] ------------[ cut here ]------------ [35903.738195] kernel BUG at include/linux/mm.h:707! [35903.738200] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI [35903.738205] CPU: 7 PID: 1024023 Comm: kworker/7:1 Not tainted 5.10.11-arch1-1 #1 [35903.738207] Hardware name: Supermicro X10SRA/X10SRA, BIOS 2.1a 10/24/2018 [35903.738213] Workqueue: zswap-shrink shrink_worker [35903.738218] RIP: 0010:__free_pages+0x83/0x90 [35903.738221] Code: 33 e4 ff ff eb d1 85 f6 75 09 5b 5d 41 5c e9 a4 fe ff ff 5b 31 d2 5d 41 5c e9 19 e4 ff ff 48 c7 c6 50 02 f4 97 e8 cd 64 fd ff <0f> 0b 5b 5d 41 5c c3 66 0f 1f 44 00 00 0f 1f 44 00 00 48 85 ff 75 [35903.738223] RSP: 0000:ffffb3f8c7b03d60 EFLAGS: 00010286 [35903.738226] RAX: 0000000000000000 RBX: ffff9c92c5556540 RCX: ffff9c9a1fbd8bb8 [35903.738227] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9c9a1fbd8bb0 [35903.738229] RBP: ffffe4264adf4980 R08: 0000000000000000 R09: ffffb3f8c7b03a60 [35903.738230] R10: ffffb3f8c7b03a58 R11: ffffffff986cb228 R12: ffffe4264adf4980 [35903.738232] R13: ffffe4264adf4988 R14: ffff9c9477d26000 R15: ffffe4264adf4988 [35903.738234] FS: 0000000000000000(0000) GS:ffff9c9a1fbc0000(0000) knlGS:0000000000000000 [35903.738236] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [35903.738238] CR2: 0000560df03c2818 CR3: 000000023b94a001 CR4: 00000000003706e0 [35903.738240] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [35903.738241] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [35903.738242] Call Trace: [35903.738251] z3fold_zpool_shrink+0x146/0x720 [35903.738256] ? sched_clock+0x5/0x10 [35903.738259] ? sched_clock_cpu+0xc/0xb0 [35903.738262] shrink_worker+0x19/0x50 [35903.738267] process_one_work+0x1d6/0x3a0 [35903.738270] worker_thread+0x4d/0x3d0 [35903.738272] ? rescuer_thread+0x410/0x410 [35903.738275] kthread+0x133/0x150 [35903.738278] ? __kthread_bind_mask+0x60/0x60 [35903.738282] ret_from_fork+0x1f/0x30 [35903.738285] Modules linked in: md4 cmac nls_utf8 cifs libarc4 dns_resolver fscache libdes tun hid_logitech_hidpp joydev mousedev hid_logitech_dj uas usb_storage intel_rapl_msr intel_rapl_common nct6775 snd_hda_codec_realtek hwmon_vid lm92 snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi snd_hda_intel snd_intel_dspcfg soundwire_intel soundwire_generic_allocation soundwire_cadence x86_pkg_temp_thermal snd_usb_audio intel_powerclamp snd_hda_codec coretemp amdgpu snd_usbmidi_lib kvm_intel snd_hda_core snd_hwdep soundwire_bus snd_rawmidi iTCO_wdt snd_seq_device intel_pmc_bxt usbhid ftdi_sio mc iTCO_vendor_support ext4 kvm snd_soc_core gpu_sched ttm irqbypass crct10dif_pclmul crc32_pclmul snd_compress ghash_clmulni_intel ac97_bus aesni_intel snd_pcm_dmaengine drm_kms_helper crc16 mbcache snd_pcm crypto_simd jbd2 cryptd glue_helper rapl i2c_i801 intel_cstate snd_timer igb bridge cec intel_uncore snd pcspkr i2c_smbus lpc_ich ioatdma syscopyarea sysfillrect i2c_algo_bit sysimgblt stp [35903.738353] soundcore fb_sys_fops dca wmi llc mac_hid drm fuse agpgart bpf_preload ip_tables x_tables btrfs blake2b_generic libcrc32c crc32c_generic crc32c_intel xor raid6_pq xhci_pci xhci_pci_renesas [35903.738375] ---[ end trace 9543e3fb37da2045 ]--- [35913.562729] RIP: 0010:__free_pages+0x83/0x90 [35913.562733] Code: 33 e4 ff ff eb d1 85 f6 75 09 5b 5d 41 5c e9 a4 fe ff ff 5b 31 d2 5d 41 5c e9 19 e4 ff ff 48 c7 c6 50 02 f4 97 e8 cd 64 fd ff <0f> 0b 5b 5d 41 5c c3 66 0f 1f 44 00 00 0f 1f 44 00 00 48 85 ff 75 [35913.562735] RSP: 0000:ffffb3f8c7b03d60 EFLAGS: 00010286 [35913.562738] RAX: 0000000000000000 RBX: ffff9c92c5556540 RCX: ffff9c9a1fbd8bb8 [35913.562740] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9c9a1fbd8bb0 [35913.562741] RBP: ffffe4264adf4980 R08: 0000000000000000 R09: ffffb3f8c7b03a60 [35913.562743] R10: ffffb3f8c7b03a58 R11: ffffffff986cb228 R12: ffffe4264adf4980 [35913.562744] R13: ffffe4264adf4988 R14: ffff9c9477d26000 R15: ffffe4264adf4988 [35913.562746] FS: 0000000000000000(0000) GS:ffff9c9a1fbc0000(0000) knlGS:0000000000000000 [35913.562748] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [35913.562750] CR2: 0000560e28746650 CR3: 000000014494a003 CR4: 00000000003706e0 [35913.562751] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [35913.562753] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
This seems to be similar to https://bugzilla.kernel.org/show_bug.cgi?id=211323 .
Probably mine a duplicate / similar as well https://bugzilla.kernel.org/show_bug.cgi?id=211653
The same happened to me: [93852.408155] page:00000000d5c7011d refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1061a2 [93852.408157] flags: 0x2ffff0000000000() [93852.408158] raw: 02ffff0000000000 fffff738066ab148 ffff8da834432170 0000000000000000 [93852.408159] raw: 0000000000000000 0000000000000011 00000000ffffffff 0000000000000000 [93852.408160] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) [93852.408165] ------------[ cut here ]------------ [93852.408166] kernel BUG at include/linux/mm.h:707! [93852.408172] invalid opcode: 0000 [#1] PREEMPT SMP PTI [93852.408173] CPU: 0 PID: 435327 Comm: kworker/0:1 Tainted: G U OE 5.10.15-arch1-1 #1 [93852.408174] Hardware name: Dell Inc. OptiPlex 7060/XXXXXX, BIOS 1.9.1 12/11/2020 [93852.408177] Workqueue: zswap-shrink shrink_worker [93852.408180] RIP: 0010:__free_pages+0x83/0x90 [93852.408182] Code: 33 e4 ff ff eb d1 85 f6 75 09 5b 5d 41 5c e9 a4 fe ff ff 5b 31 d2 5d 41 5c e9 19 e4 ff ff 48 c7 c6 58 b7 d3 8d e8 cd 64 fd ff <0f> 0b 5b 5d 41 5c c3 66 0f 1f 44 00 00 0f 1f 44 00 00 48 85 ff 75 [93852.408183] RSP: 0018:ffffa51784a9bd60 EFLAGS: 00010286 [93852.408184] RAX: 0000000000000000 RBX: ffff8da6c0cf4780 RCX: ffff8da834418bb8 [93852.408185] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8da834418bb0 [93852.408185] RBP: fffff73804186880 R08: 0000000000000000 R09: ffffa51784a9ba60 [93852.408186] R10: ffffa51784a9ba58 R11: ffffffff8e4cb228 R12: fffff73804186880 [93852.408187] R13: fffff73804186888 R14: ffff8da6c61a2000 R15: fffff73804186888 [93852.408188] FS: 0000000000000000(0000) GS:ffff8da834400000(0000) knlGS:0000000000000000 [93852.408189] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [93852.408190] CR2: 0000021611de5000 CR3: 0000000142ae2004 CR4: 00000000003726f0 [93852.408191] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [93852.408191] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [93852.408192] Call Trace: [93852.408196] z3fold_zpool_shrink+0x146/0x720 [93852.408199] ? sched_clock+0x5/0x10 [93852.408201] ? sched_clock_cpu+0xc/0xb0 [93852.408203] shrink_worker+0x19/0x50 [93852.408206] process_one_work+0x1d6/0x3a0 [93852.408208] worker_thread+0x4d/0x3d0 [93852.408209] ? rescuer_thread+0x3c0/0x3c0 [93852.408210] kthread+0x133/0x150 [93852.408212] ? __kthread_bind_mask+0x60/0x60 [93852.408214] ret_from_fork+0x22/0x30 [93852.408216] Modules linked in: vhost_net vhost vhost_iotlb tap tun xt_CHECKSUM xt_MASQUERADE bridge stp llc nfnetlink xt_nat wireguard curve25519_x86_64 libchacha20poly1305 chacha_x86_64 poly1305_x86_64 libblake2s blake2s_x86_64 ip6_udp_tunnel udp_tunnel libcurve25519_generic libchacha libblake2s_generic exfat rfcomm xt_multiport xt_cgroup xt_mark xt_owner ip6table_raw iptable_raw ip6table_mangle iptable_mangle ip6table_nat iptable_nat cmac algif_hash algif_skcipher af_alg bnep nls_iso8859_1 vfat fat snd_hda_codec_hdmi intel_rapl_msr intel_rapl_common snd_sof_pci snd_sof_intel_byt snd_sof_intel_ipc snd_sof_intel_hda_common snd_soc_hdac_hda snd_sof_xtensa_dsp snd_sof_intel_hda snd_hda_codec_realtek snd_sof snd_hda_codec_generic ledtrig_audio snd_soc_skl snd_soc_sst_ipc snd_soc_sst_dsp snd_hda_ext_core snd_soc_acpi_intel_match snd_soc_acpi snd_hda_intel snd_intel_dspcfg soundwire_intel soundwire_generic_allocation soundwire_cadence x86_pkg_temp_thermal intel_powerclamp coretemp ee1004 [93852.408246] iTCO_wdt snd_hda_codec intel_pmc_bxt iTCO_vendor_support snd_hda_core mei_hdcp mei_wdt snd_hwdep kvm_intel dell_wmi_aio soundwire_bus dell_wmi dell_smbios dell_wmi_descriptor intel_wmi_thunderbolt sparse_keymap wmi_bmof snd_soc_core kvm dcdbas snd_compress ac97_bus snd_pcm_dmaengine nf_log_ipv6 ip6t_REJECT nf_reject_ipv6 snd_pcm irqbypass btusb rapl btrtl snd_timer intel_cstate intel_uncore i2c_i801 btbcm btintel xt_hl snd 88XXau(OE) pcspkr e1000e soundcore i2c_smbus bluetooth ip6t_rt mei_me ecdh_generic intel_lpss_pci mousedev cfg80211 intel_lpss uas rfkill ecc mei idma64 intel_pch_thermal nf_log_ipv4 nf_log_common ipt_REJECT nf_reject_ipv4 xt_LOG tpm_crb wmi xt_limit xt_addrtype tpm_tis xt_tcpudp tpm_tis_core acpi_pad mac_hid xt_conntrack ip6table_filter ip6_tables nf_conntrack_netbios_ns nf_conntrack_broadcast nf_nat_ftp nf_nat nf_conntrack_ftp nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c iptable_filter sg crypto_user fuse bpf_preload ip_tables x_tables ext4 [93852.408283] crc32c_generic crc16 mbcache jbd2 usb_storage hid_logitech_hidpp hid_logitech_dj usbhid dm_crypt cbc encrypted_keys dm_mod trusted tpm rng_core crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd glue_helper sr_mod cdrom xhci_pci xhci_pci_renesas i915 video intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec drm agpgart [93852.408300] ---[ end trace 8b8f71d7e7f2bc26 ]--- [93852.408822] ------------[ cut here ]------------ [93852.408826] WARNING: CPU: 0 PID: 435327 at kernel/rcu/tree_plugin.h:297 rcu_note_context_switch+0x42/0x480 [93852.408826] Modules linked in: vhost_net vhost vhost_iotlb tap tun xt_CHECKSUM xt_MASQUERADE bridge stp llc nfnetlink xt_nat wireguard curve25519_x86_64 libchacha20poly1305 chacha_x86_64 poly1305_x86_64 libblake2s blake2s_x86_64 ip6_udp_tunnel udp_tunnel libcurve25519_generic libchacha libblake2s_generic exfat rfcomm xt_multiport xt_cgroup xt_mark xt_owner ip6table_raw iptable_raw ip6table_mangle iptable_mangle ip6table_nat iptable_nat cmac algif_hash algif_skcipher af_alg bnep nls_iso8859_1 vfat fat snd_hda_codec_hdmi intel_rapl_msr intel_rapl_common snd_sof_pci snd_sof_intel_byt snd_sof_intel_ipc snd_sof_intel_hda_common snd_soc_hdac_hda snd_sof_xtensa_dsp snd_sof_intel_hda snd_hda_codec_realtek snd_sof snd_hda_codec_generic ledtrig_audio snd_soc_skl snd_soc_sst_ipc snd_soc_sst_dsp snd_hda_ext_core snd_soc_acpi_intel_match snd_soc_acpi snd_hda_intel snd_intel_dspcfg soundwire_intel soundwire_generic_allocation soundwire_cadence x86_pkg_temp_thermal intel_powerclamp coretemp ee1004 [93852.408855] iTCO_wdt snd_hda_codec intel_pmc_bxt iTCO_vendor_support snd_hda_core mei_hdcp mei_wdt snd_hwdep kvm_intel dell_wmi_aio soundwire_bus dell_wmi dell_smbios dell_wmi_descriptor intel_wmi_thunderbolt sparse_keymap wmi_bmof snd_soc_core kvm dcdbas snd_compress ac97_bus snd_pcm_dmaengine nf_log_ipv6 ip6t_REJECT nf_reject_ipv6 snd_pcm irqbypass btusb rapl btrtl snd_timer intel_cstate intel_uncore i2c_i801 btbcm btintel xt_hl snd 88XXau(OE) pcspkr e1000e soundcore i2c_smbus bluetooth ip6t_rt mei_me ecdh_generic intel_lpss_pci mousedev cfg80211 intel_lpss uas rfkill ecc mei idma64 intel_pch_thermal nf_log_ipv4 nf_log_common ipt_REJECT nf_reject_ipv4 xt_LOG tpm_crb wmi xt_limit xt_addrtype tpm_tis xt_tcpudp tpm_tis_core acpi_pad mac_hid xt_conntrack ip6table_filter ip6_tables nf_conntrack_netbios_ns nf_conntrack_broadcast nf_nat_ftp nf_nat nf_conntrack_ftp nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 libcrc32c iptable_filter sg crypto_user fuse bpf_preload ip_tables x_tables ext4 [93852.409675] crc32c_generic crc16 mbcache jbd2 usb_storage hid_logitech_hidpp hid_logitech_dj usbhid dm_crypt cbc encrypted_keys dm_mod trusted tpm rng_core crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel aesni_intel crypto_simd cryptd glue_helper sr_mod cdrom xhci_pci xhci_pci_renesas i915 video intel_gtt i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec drm agpgart [93852.409693] CPU: 0 PID: 435327 Comm: kworker/0:1 Tainted: G UD OE 5.10.15-arch1-1 #1 [93852.409694] Hardware name: Dell Inc. OptiPlex 7060/XXXXXX, BIOS 1.9.1 12/11/2020 [93852.409698] Workqueue: zswap-shrink shrink_worker [93852.409701] RIP: 0010:rcu_note_context_switch+0x42/0x480 [93852.409702] Code: c3 40 cf 02 00 65 48 03 1d 13 eb 4f 73 0f 1f 44 00 00 40 84 ed 75 15 65 48 8b 04 25 c0 7b 01 00 8b 90 b0 03 00 00 85 d2 7e 02 <0f> 0b 65 48 8b 04 25 c0 7b 01 00 8b 80 b0 03 00 00 85 c0 7e 0a 41 [93852.409703] RSP: 0018:ffffa51784a9b7b0 EFLAGS: 00010002 [93852.409704] RAX: ffff8da5c7a8be80 RBX: ffff8da83442cf40 RCX: 0000000000000000 [93852.409704] RDX: 0000000000000001 RSI: ffffffff8d46b02b RDI: 0000000000000000 [93852.409705] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000400 [93852.409706] R10: abcc77118461cefd R11: ffffa51784a9ba9f R12: 000000000002c180 [93852.409707] R13: ffff8da5c7a8be80 R14: ffff8da5c7a8be80 R15: ffff8da83442c180 [93852.409708] FS: 0000000000000000(0000) GS:ffff8da834400000(0000) knlGS:0000000000000000 [93852.409709] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [93852.409709] CR2: 0000021611de5000 CR3: 0000000142ae2004 CR4: 00000000003726f0 [93852.409710] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [93852.409711] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [93852.409712] Call Trace: [93852.409716] __schedule+0xae/0x810 [93852.409718] schedule+0x5b/0xc0 [93852.409720] schedule_timeout+0x11c/0x160 [93852.409721] wait_for_completion+0x9e/0x100 [93852.409725] virt_efi_query_variable_info+0x141/0x150 [93852.409728] efi_query_variable_store+0x7b/0x1e0 [93852.409731] ? vsnprintf+0x6e/0x4f0 [93852.409733] efivar_entry_set_safe+0xbd/0x210 [93852.409734] efi_pstore_write+0x12d/0x1a0 [93852.409738] pstore_dump+0x1b3/0x2f0 [93852.409741] kmsg_dump+0xa8/0xd0 [93852.409743] oops_end+0x61/0xd0 [93852.409745] do_trap+0x8d/0x110 [93852.409747] ? __free_pages+0x83/0x90 [93852.409749] do_error_trap+0x64/0xa0 [93852.409750] ? __free_pages+0x83/0x90 [93852.409752] exc_invalid_op+0x4e/0x70 [93852.409753] ? __free_pages+0x83/0x90 [93852.409755] asm_exc_invalid_op+0x12/0x20 [93852.409757] RIP: 0010:__free_pages+0x83/0x90 [93852.409758] Code: 33 e4 ff ff eb d1 85 f6 75 09 5b 5d 41 5c e9 a4 fe ff ff 5b 31 d2 5d 41 5c e9 19 e4 ff ff 48 c7 c6 58 b7 d3 8d e8 cd 64 fd ff <0f> 0b 5b 5d 41 5c c3 66 0f 1f 44 00 00 0f 1f 44 00 00 48 85 ff 75 [93852.409759] RSP: 0018:ffffa51784a9bd60 EFLAGS: 00010286 [93852.409760] RAX: 0000000000000000 RBX: ffff8da6c0cf4780 RCX: ffff8da834418bb8 [93852.409761] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8da834418bb0 [93852.409762] RBP: fffff73804186880 R08: 0000000000000000 R09: ffffa51784a9ba60 [93852.409762] R10: ffffa51784a9ba58 R11: ffffffff8e4cb228 R12: fffff73804186880 [93852.409763] R13: fffff73804186888 R14: ffff8da6c61a2000 R15: fffff73804186888 [93852.409767] z3fold_zpool_shrink+0x146/0x720 [93852.409769] ? sched_clock+0x5/0x10 [93852.409770] ? sched_clock_cpu+0xc/0xb0 [93852.409772] shrink_worker+0x19/0x50 [93852.409774] process_one_work+0x1d6/0x3a0 [93852.409776] worker_thread+0x4d/0x3d0 [93852.409777] ? rescuer_thread+0x3c0/0x3c0 [93852.409779] kthread+0x133/0x150 [93852.409781] ? __kthread_bind_mask+0x60/0x60 [93852.409783] ret_from_fork+0x22/0x30 [93852.409784] ---[ end trace 8b8f71d7e7f2bc27 ]--- [93853.447493] RIP: 0010:__free_pages+0x83/0x90 [93853.447502] Code: 33 e4 ff ff eb d1 85 f6 75 09 5b 5d 41 5c e9 a4 fe ff ff 5b 31 d2 5d 41 5c e9 19 e4 ff ff 48 c7 c6 58 b7 d3 8d e8 cd 64 fd ff <0f> 0b 5b 5d 41 5c c3 66 0f 1f 44 00 00 0f 1f 44 00 00 48 85 ff 75 [93853.447503] RSP: 0018:ffffa51784a9bd60 EFLAGS: 00010286 [93853.447505] RAX: 0000000000000000 RBX: ffff8da6c0cf4780 RCX: ffff8da834418bb8 [93853.447506] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8da834418bb0 [93853.447506] RBP: fffff73804186880 R08: 0000000000000000 R09: ffffa51784a9ba60 [93853.447507] R10: ffffa51784a9ba58 R11: ffffffff8e4cb228 R12: fffff73804186880 [93853.447508] R13: fffff73804186888 R14: ffff8da6c61a2000 R15: fffff73804186888 [93853.447510] FS: 0000000000000000(0000) GS:ffff8da834400000(0000) knlGS:0000000000000000 [93853.447511] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [93853.447511] CR2: 000056546562d630 CR3: 000000012356e004 CR4: 00000000003726f0 [93853.447512] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [93853.447513] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Created attachment 295405 [details] dmesg output Bug happened when tried to stop java process. It was heavily using swap, and the process could not be killed. System was half-frozen: sudo and doas were not giving any prompt to enter the password, terminal emulators will just freeze when 'exit' was executed. 'cat /proc/version' yields output 'Linux version 5.10.16-arch1-1 (linux@archlinux) (gcc (GCC) 10.2.0, GNU ld (GNU Binutils) 2.36) #1 SMP PREEMPT Sat, 13 Feb 2021 20:50:18 +0000'