Laptop freezes after kernel bug

My laptop has frozen two times after updating to kernel 5.13.4. Each time crash was preceded by this kernel bug:

июл 27 14:08:03 laptop kernel: list_del corruption. prev->next should be ffff98679438a5d0, but was ca53e83f5e8cf5a8
июл 27 14:08:04 laptop kernel: ------------[ cut here ]------------
июл 27 14:08:04 laptop kernel: kernel BUG at lib/list_debug.c:51!
июл 27 14:08:04 laptop kernel: invalid opcode: 0000 [#1] SMP PTI
июл 27 14:08:04 laptop kernel: CPU: 4 PID: 148 Comm: kswapd0 Tainted: P           OE     5.13.4-200.fc34.x86_64 #1
июл 27 14:08:04 laptop kernel: Hardware name: ASUSTeK COMPUTER INC. N551JM/N551JM, BIOS N551JM.204 10/06/2014
июл 27 14:08:04 laptop kernel: RIP: 0010:__list_del_entry_valid.cold+0x31/0x47
июл 27 14:08:04 laptop kernel: Code: 44 62 a7 e8 21 27 fe ff 0f 0b 48 c7 c7 30 45 62 a7 e8 13 27 fe ff 0f 0b 48 89 f2 48 89 fe 48 c7 c7 f0 44 62 a7 e8 ff 26 fe ff <0f> 0b 48 89 fe 4c 89 c2 48 c7 c7 b8 44 62 a7 e8 eb 26 fe ff 0f 0b
июл 27 14:08:04 laptop kernel: RSP: 0018:ffffb7cd010bfb88 EFLAGS: 00010282
июл 27 14:08:04 laptop kernel: RAX: 0000000000000054 RBX: ffff9869995e4540 RCX: 0000000000000000
июл 27 14:08:04 laptop kernel: RDX: ffff986a22f26840 RSI: ffff986a22f18a00 RDI: ffff986a22f18a00
июл 27 14:08:04 laptop kernel: RBP: ffff98679438a540 R08: 0000000000000000 R09: ffffb7cd010bf9c8
июл 27 14:08:04 laptop kernel: R10: ffffb7cd010bf9c0 R11: ffffffffa7d468c8 R12: ffff98679438a598
июл 27 14:08:04 laptop kernel: R13: ffff98679438a598 R14: ffff98680bf87870 R15: 0000000000000400
июл 27 14:08:04 laptop kernel: FS:  0000000000000000(0000) GS:ffff986a22f00000(0000) knlGS:0000000000000000
июл 27 14:08:04 laptop kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
июл 27 14:08:04 laptop kernel: CR2: 00007fcd74641ffc CR3: 000000012cc10005 CR4: 00000000001706e0
июл 27 14:08:04 laptop kernel: Call Trace:
июл 27 14:08:04 laptop kernel:  __dentry_kill+0x89/0x180
июл 27 14:08:04 laptop kernel:  shrink_dentry_list+0x4e/0xc0
июл 27 14:08:04 laptop kernel:  prune_dcache_sb+0x44/0x50
июл 27 14:08:04 laptop kernel:  super_cache_scan+0x12f/0x1f0
июл 27 14:08:04 laptop kernel:  do_shrink_slab+0x13e/0x2b0
июл 27 14:08:04 laptop kernel:  shrink_slab+0x168/0x280
июл 27 14:08:04 laptop kernel:  shrink_node+0x2c8/0x6e0
июл 27 14:08:04 laptop kernel:  balance_pgdat+0x2fa/0x620
июл 27 14:08:04 laptop kernel:  kswapd+0x1e6/0x360
июл 27 14:08:04 laptop kernel:  ? finish_wait+0x80/0x80
июл 27 14:08:04 laptop kernel:  ? balance_pgdat+0x620/0x620
июл 27 14:08:04 laptop kernel:  kthread+0x127/0x150
июл 27 14:08:04 laptop kernel:  ? set_kthread_struct+0x40/0x40
июл 27 14:08:04 laptop kernel:  ret_from_fork+0x22/0x30
июл 27 14:08:04 laptop kernel: Modules linked in: uinput rfcomm snd_seq_dummy snd_hrtimer xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_nat_tftp nft_objref nf_conntrack_tftp bridge stp llc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nf>
июл 27 14:08:04 laptop kernel:  snd_hwdep btbcm snd_seq mc coretemp btintel iTCO_wdt mei_hdcp kvm_intel bluetooth kvm intel_pmc_bxt libarc4 irqbypass rapl intel_cstate intel_uncore snd_seq_device iTCO_vendor_support snd_pcm at24 snd_time>
июл 27 14:08:04 laptop kernel: ---[ end trace 02a4d6cfba88ccd8 ]---
июл 27 14:08:04 laptop kernel: RIP: 0010:__list_del_entry_valid.cold+0x31/0x47
июл 27 14:08:04 laptop kernel: Code: 44 62 a7 e8 21 27 fe ff 0f 0b 48 c7 c7 30 45 62 a7 e8 13 27 fe ff 0f 0b 48 89 f2 48 89 fe 48 c7 c7 f0 44 62 a7 e8 ff 26 fe ff <0f> 0b 48 89 fe 4c 89 c2 48 c7 c7 b8 44 62 a7 e8 eb 26 fe ff 0f 0b
июл 27 14:08:04 laptop kernel: RSP: 0018:ffffb7cd010bfb88 EFLAGS: 00010282
июл 27 14:08:04 laptop kernel: RAX: 0000000000000054 RBX: ffff9869995e4540 RCX: 0000000000000000
июл 27 14:08:04 laptop kernel: RDX: ffff986a22f26840 RSI: ffff986a22f18a00 RDI: ffff986a22f18a00
июл 27 14:08:04 laptop kernel: RBP: ffff98679438a540 R08: 0000000000000000 R09: ffffb7cd010bf9c8
июл 27 14:08:04 laptop kernel: R10: ffffb7cd010bf9c0 R11: ffffffffa7d468c8 R12: ffff98679438a598
июл 27 14:08:04 laptop kernel: R13: ffff98679438a598 R14: ffff98680bf87870 R15: 0000000000000400
июл 27 14:08:04 laptop kernel: FS:  0000000000000000(0000) GS:ffff986a22f00000(0000) knlGS:0000000000000000
июл 27 14:08:04 laptop kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
июл 27 14:08:04 laptop kernel: CR2: 00007fcd74641ffc CR3: 000000012cc10005 CR4: 00000000001706e0

lspci:

00:00.0 Host bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor DRAM Controller (rev 06)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor PCI Express x16 Controller (rev 06)
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
00:03.0 Audio device: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor HD Audio Controller (rev 06)
00:14.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI (rev 05)
00:16.0 Communication controller: Intel Corporation 8 Series/C220 Series Chipset Family MEI Controller #1 (rev 04)
00:1a.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #2 (rev 05)
00:1b.0 Audio device: Intel Corporation 8 Series/C220 Series Chipset High Definition Audio Controller (rev 05)
00:1c.0 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #1 (rev d5)
00:1c.1 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #2 (rev d5)
00:1c.2 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #3 (rev d5)
00:1c.3 PCI bridge: Intel Corporation 8 Series/C220 Series Chipset Family PCI Express Root Port #4 (rev d5)
00:1d.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #1 (rev 05)
00:1f.0 ISA bridge: Intel Corporation HM86 Express LPC Controller (rev 05)
00:1f.2 SATA controller: Intel Corporation 8 Series/C220 Series Chipset Family 6-port SATA Controller 1 [AHCI mode] (rev 05)
00:1f.3 SMBus: Intel Corporation 8 Series/C220 Series Chipset Family SMBus Controller (rev 05)
01:00.0 3D controller: NVIDIA Corporation GM107M [GeForce GTX 860M] (rev a2)
04:00.0 Network controller: Qualcomm Atheros AR9485 Wireless Network Adapter (rev 01)
05:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTL8411B PCI Express Card Reader (rev 01)
05:00.1 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 12)

Each time I couldn’t login using another VT, but I was able to reboot computer using REISUB key combination.

Does anyone have a similar problem?

Today there was another kernel oops. It occured during resuming from sleep. After 30 minutes, laptop froze (it occured when I tried to launch Firefox).

авг 04 18:49:30 kernel: BUG: unable to handle page fault for address: 000000005efcef90
авг 04 18:49:30 kernel: #PF: supervisor read access in kernel mode
авг 04 18:49:30 kernel: #PF: error_code(0x0000) - not-present page
авг 04 18:49:30 kernel: PGD 0 P4D 0 
авг 04 18:49:30 kernel: Oops: 0000 [#1] SMP PTI
авг 04 18:49:30 kernel: CPU: 7 PID: 147 Comm: kswapd0 Tainted: P           OE     5.13.6-200.fc34.x86_64 #1
авг 04 18:49:30 kernel: Hardware name: ASUSTeK COMPUTER INC. N551JM/N551JM, BIOS N551JM.204 10/06/2014
авг 04 18:49:30 kernel: RIP: 0010:locks_free_lock_context+0x20/0x70
авг 04 18:49:30 kernel: Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 56 41 55 41 54 55 48 8b af 70 01 00 00 48 85 ed 75 08 5d 41 5c 41 5d 41 5e c3 <48> 8b 45 08 4c 8d 75 08 4c 8d 6d 18 4c 8d 65 28 49 39 c6 0f 85 06
авг 04 18:49:30 kernel: RSP: 0018:ffffae2dc10c7b68 EFLAGS: 00010206
авг 04 18:49:30 kernel: RAX: 0000000000000000 RBX: ffff90649438a168 RCX: 0000000000000000
авг 04 18:49:30 kernel: RDX: 0000000000032e00 RSI: 0000000000000000 RDI: ffff90649438a168
авг 04 18:49:30 kernel: RBP: 000000005efcef88 R08: 0000000000000000 R09: ffff9064943a2708
авг 04 18:49:30 kernel: R10: 0000000000000000 R11: 0000000000000000 R12: ffff90649438a168
авг 04 18:49:30 kernel: R13: ffff906502ee8800 R14: ffff906502ee8870 R15: 000000000c24a400
авг 04 18:49:30 kernel: FS:  0000000000000000(0000) GS:ffff906722fc0000(0000) knlGS:0000000000000000
авг 04 18:49:30 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
авг 04 18:49:30 kernel: CR2: 000000005efcef90 CR3: 000000010cc10002 CR4: 00000000001706e0
авг 04 18:49:30 kernel: Call Trace:
авг 04 18:49:30 kernel:  __destroy_inode+0x80/0x170
авг 04 18:49:30 kernel:  destroy_inode+0x2a/0x70
авг 04 18:49:30 kernel:  dispose_list+0x48/0x60
авг 04 18:49:30 kernel:  prune_icache_sb+0x44/0x50
авг 04 18:49:30 kernel:  super_cache_scan+0x161/0x1f0
авг 04 18:49:30 kernel:  do_shrink_slab+0x13e/0x2b0
авг 04 18:49:30 kernel:  shrink_slab+0x168/0x280
авг 04 18:49:30 kernel:  shrink_node+0x2c8/0x6e0
авг 04 18:49:30 kernel:  balance_pgdat+0x2fa/0x620
авг 04 18:49:30 kernel:  kswapd+0x1e6/0x360
авг 04 18:49:30 kernel:  ? finish_wait+0x80/0x80
авг 04 18:49:30 kernel:  ? balance_pgdat+0x620/0x620
авг 04 18:49:30 kernel:  kthread+0x127/0x150
авг 04 18:49:30 kernel:  ? set_kthread_struct+0x40/0x40
авг 04 18:49:30 kernel:  ret_from_fork+0x22/0x30
авг 04 18:49:30 kernel: Modules linked in: uinput rfcomm snd_seq_dummy snd_hrtimer xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_nat_tftp nft_objref nf_conntrack_tftp bridge stp llc nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_raw iptable_security ip_set nf_tables nfnetlink ip6table_filter ip6_tables iptable_filter bnep sunrpc vfat fat nvidia_drm(POE) nvidia_modeset(POE) nvidia_uvm(POE) nvidia(POE) intel_rapl_msr intel_rapl_common uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_v4l2 videobuf2_common x86_pkg_temp_thermal videodev mc intel_powerclamp ath3k coretemp btusb asus_nb_wmi asus_wmi btrtl btbcm btintel sparse_keymap kvm_intel snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi snd_hda_intel snd_intel_dspcfg mei_hdcp
авг 04 18:49:30 kernel:  snd_intel_sdw_acpi kvm snd_hda_codec ath9k ath9k_common ath9k_hw snd_hda_core snd_hwdep snd_seq mac80211 at24 ath i2c_i801 cfg80211 snd_seq_device snd_pcm iTCO_wdt intel_pmc_bxt irqbypass iTCO_vendor_support snd_timer mei_me rapl bluetooth intel_cstate snd mei lpc_ich i2c_smbus libarc4 rfkill intel_uncore soundcore asus_wireless pcspkr joydev zram ip_tables i915 rtsx_pci_sdmmc mmc_core mxm_wmi crct10dif_pclmul crc32_pclmul crc32c_intel i2c_algo_bit drm_kms_helper ghash_clmulni_intel cec drm serio_raw rtsx_pci r8169 wmi video fuse
авг 04 18:49:30 kernel: CR2: 000000005efcef90
авг 04 18:49:30 kernel: ---[ end trace 0e17b3494ae8ae7d ]---
авг 04 18:49:30 kernel: RIP: 0010:locks_free_lock_context+0x20/0x70
авг 04 18:49:30 kernel: Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 56 41 55 41 54 55 48 8b af 70 01 00 00 48 85 ed 75 08 5d 41 5c 41 5d 41 5e c3 <48> 8b 45 08 4c 8d 75 08 4c 8d 6d 18 4c 8d 65 28 49 39 c6 0f 85 06
авг 04 18:49:30 kernel: RSP: 0018:ffffae2dc10c7b68 EFLAGS: 00010206
авг 04 18:49:30 kernel: RAX: 0000000000000000 RBX: ffff90649438a168 RCX: 0000000000000000
авг 04 18:49:30 kernel: RDX: 0000000000032e00 RSI: 0000000000000000 RDI: ffff90649438a168
авг 04 18:49:30 kernel: RBP: 000000005efcef88 R08: 0000000000000000 R09: ffff9064943a2708
авг 04 18:49:30 kernel: R10: 0000000000000000 R11: 0000000000000000 R12: ffff90649438a168
авг 04 18:49:30 kernel: R13: ffff906502ee8800 R14: ffff906502ee8870 R15: 000000000c24a400
авг 04 18:49:30 kernel: FS:  0000000000000000(0000) GS:ffff906722fc0000(0000) knlGS:0000000000000000
авг 04 18:49:30 kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
авг 04 18:49:30 kernel: CR2: 000000005efcef90 CR3: 000000010cc10002 CR4: 00000000001706e0

There is a new kernel update:

$ uname -a
Linux k 5.13.6-200.fc34.x86_64 #1 SMP Wed Jul 28 15:31:21 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

Please see if this is better.

Latest crash occurred with this kernel((

Do you know what is the last known good kernel version for your machine?

You can keep using a good version while waiting for further updates. It will help if you can file a bug to bugzilla.redhat.com .

there is a new kernel. see and how to install:
https://bodhi.fedoraproject.org/updates/FEDORA-2021-d691189758

1 Like

The last working kernel was 5.12.17. My kernel is tainted (NVIDIA proprietary driver), so bugreport is unlikely to be considered.

1 Like

yup, but only with proprietary driver installed.

two ways to go:

  • leave it as is and wait (maybe without let the box go to sleep, only poweroff)
  • remove nvidia stuff and find out if the kernel then plays well, if not => bugreport
    for the bugreport test the “resume from sleep”-case too
2 Likes

I have removed NVIDIA driver and this bug disappeared for a while. But today it occurred again:

авг 20 19:13:49 laptop kernel: BUG: unable to handle page fault for address: 00000000ca544fe0
авг 20 19:13:49 laptop kernel: #PF: supervisor read access in kernel mode
авг 20 19:13:49 laptop kernel: #PF: error_code(0x0000) - not-present page
авг 20 19:13:49 laptop kernel: PGD 0 P4D 0 
авг 20 19:13:49 laptop kernel: Oops: 0000 [#1] SMP PTI
авг 20 19:13:49 laptop kernel: CPU: 1 PID: 140 Comm: kswapd0 Not tainted 5.13.10-200.fc34.x86_64 #1
авг 20 19:13:49 laptop kernel: Hardware name: ASUSTeK COMPUTER INC. N551JM/N551JM, BIOS N551JM.204 10/06/2014
авг 20 19:13:49 laptop kernel: RIP: 0010:locks_free_lock_context+0x20/0x70
авг 20 19:13:49 laptop kernel: Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 56 41 55 41 54 55 48 8b af 70 01 00 00 48 85 ed 75 08 5d 41 5c 41 5d 41 5e c3 <48> 8b 45 08 4c 8d 75 08 4c 8d 6d 18 4c 8d 65 28 49 39 c6 0f 85 66
авг 20 19:13:49 laptop kernel: RSP: 0018:ffffa8f7c108fb68 EFLAGS: 00010206
авг 20 19:13:49 laptop kernel: RAX: 0000000000000000 RBX: ffff9ae75438a168 RCX: 0000000000000000
авг 20 19:13:49 laptop kernel: RDX: 0000000000032e00 RSI: 0000000000000000 RDI: ffff9ae75438a168
авг 20 19:13:49 laptop kernel: RBP: 00000000ca544fd8 R08: 0000000000000000 R09: ffff9ae73b43d060
авг 20 19:13:49 laptop kernel: R10: 0000000000000000 R11: 0000000000000000 R12: ffff9ae75438a168
авг 20 19:13:49 laptop kernel: R13: ffff9ae7c86ee000 R14: ffff9ae7c86ee070 R15: 000000000d8e2800
авг 20 19:13:49 laptop kernel: FS:  0000000000000000(0000) GS:ffff9ae9e2e40000(0000) knlGS:0000000000000000
авг 20 19:13:49 laptop kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
авг 20 19:13:49 laptop kernel: CR2: 00000000ca544fe0 CR3: 000000013bc10005 CR4: 00000000001706e0
авг 20 19:13:49 laptop kernel: Call Trace:
авг 20 19:13:49 laptop kernel:  __destroy_inode+0x80/0x170
авг 20 19:13:49 laptop kernel:  destroy_inode+0x2a/0x70
авг 20 19:13:49 laptop kernel:  dispose_list+0x48/0x60
авг 20 19:13:49 laptop kernel:  prune_icache_sb+0x44/0x50
авг 20 19:13:49 laptop kernel:  super_cache_scan+0x161/0x1f0
авг 20 19:13:49 laptop kernel:  do_shrink_slab+0x13e/0x2b0
авг 20 19:13:49 laptop kernel:  shrink_slab+0x168/0x280
авг 20 19:13:49 laptop kernel:  shrink_node+0x2c8/0x6e0
авг 20 19:13:49 laptop kernel:  balance_pgdat+0x2fa/0x620
авг 20 19:13:49 laptop kernel:  kswapd+0x1e6/0x360
авг 20 19:13:49 laptop kernel:  ? finish_wait+0x80/0x80
авг 20 19:13:49 laptop kernel:  ? balance_pgdat+0x620/0x620
авг 20 19:13:49 laptop kernel:  kthread+0x127/0x150
авг 20 19:13:49 laptop kernel:  ? set_kthread_struct+0x40/0x40
авг 20 19:13:49 laptop kernel:  ret_from_fork+0x22/0x30
авг 20 19:13:49 laptop kernel: Modules linked in: uas usb_storage ipheth apple_mfi_fastcharge rfcomm uinput snd_seq_dummy snd_hrtimer xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_nat_tftp nft_objref nf_conntrack_tftp bridge stp l>
авг 20 19:13:49 laptop kernel:  snd_hda_codec_hdmi snd_hda_intel snd_intel_dspcfg snd_intel_sdw_acpi snd_hda_codec snd_hda_core snd_hwdep snd_seq rapl snd_seq_device intel_cstate snd_pcm snd_timer snd soundcore mc asus_nb_wmi asus_wmi sp>
авг 20 19:13:49 laptop kernel: CR2: 00000000ca544fe0
авг 20 19:13:49 laptop kernel: ---[ end trace abfa5437c32cb330 ]---
авг 20 19:13:49 laptop kernel: RIP: 0010:locks_free_lock_context+0x20/0x70
авг 20 19:13:49 laptop kernel: Code: 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 56 41 55 41 54 55 48 8b af 70 01 00 00 48 85 ed 75 08 5d 41 5c 41 5d 41 5e c3 <48> 8b 45 08 4c 8d 75 08 4c 8d 6d 18 4c 8d 65 28 49 39 c6 0f 85 66
авг 20 19:13:49 laptop kernel: RSP: 0018:ffffa8f7c108fb68 EFLAGS: 00010206
авг 20 19:13:49 laptop kernel: RAX: 0000000000000000 RBX: ffff9ae75438a168 RCX: 0000000000000000
авг 20 19:13:49 laptop kernel: RDX: 0000000000032e00 RSI: 0000000000000000 RDI: ffff9ae75438a168
авг 20 19:13:49 laptop kernel: RBP: 00000000ca544fd8 R08: 0000000000000000 R09: ffff9ae73b43d060
авг 20 19:13:49 laptop kernel: R10: 0000000000000000 R11: 0000000000000000 R12: ffff9ae75438a168
авг 20 19:13:49 laptop kernel: R13: ffff9ae7c86ee000 R14: ffff9ae7c86ee070 R15: 000000000d8e2800
авг 20 19:13:49 laptop kernel: FS:  0000000000000000(0000) GS:ffff9ae9e2e40000(0000) knlGS:0000000000000000
авг 20 19:13:49 laptop kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
авг 20 19:13:49 laptop kernel: CR2: 00000000ca544fe0 CR3: 000000013bc10005 CR4: 00000000001706e0

I have posted the bug report at https://bugzilla.redhat.com/show_bug.cgi?id=1996302.

This issue seems to be fixed in the 5.13.13 kernel.