Kubuntu freezes due to "unable to handle kernel NULL pointer" when moving to Screen Energy Saving

[Ilya Brik]

Description: Ubuntu 18.04.1 LTS
Release: 18.04

This issue manifested today after upgrading the kernel from 4.15.0-43 to 4.15.0-44.
Reproduction scenario:

Laptop Dell Inc. Latitude E7470/0T6HHJ, BIOS 1.6.3 06/15/2016 is connected to Dock Station which is connected to 2 external displays. Laptop's display is closed.

Configure Energy Saving as following:
Dim screen: 1 min
Screen Energy Saving: 1 min

Lock the display (Ctrl-Alt-L) and wait for 3-4 minutes - the displays turn off.

Move a mouse / click on a keyboard

Expected result:
Displays turn on

Actual result:
Displays remain off.

After looking into the journalctl --system's output I found the error below observed exactly when the Screen Energy Saving turned on:

Jan 30 10:19:46 akaars-kubuntu kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000245
Jan 30 10:19:46 akaars-kubuntu kernel: IP: intel_ddi_post_disable+0x54/0x170 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: PGD 0 P4D 0
Jan 30 10:19:46 akaars-kubuntu kernel: Oops: 0000 [#1] SMP PTI
Jan 30 10:19:46 akaars-kubuntu kernel: Modules linked in: ip6table_filter ip6_tables ipt_MASQUERADE nf_nat_masquerade_ipv4 nf_conntrack_netlink nfnetlink xfrm_user xfrm_algo iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 xt_addrtype xt_conntrack nf_nat nf_connt
Jan 30 10:19:46 akaars-kubuntu kernel: snd_hda_codec irqbypass dell_smm_hwmon snd_hda_core crct10dif_pclmul snd_hwdep crc32_pclmul ghash_clmulni_intel snd_pcm pcbc snd_seq_midi snd_seq_midi_event aesni_intel btusb aes_x86_64 btrtl crypto_simd btbcm iwlmvm glue_helper bt
Jan 30 10:19:46 akaars-kubuntu kernel: lp parport ip_tables x_tables autofs4 hid_generic usbhid hid rtsx_pci_sdmmc i915 e1000e i2c_algo_bit drm_kms_helper syscopyarea sysfillrect nvme ptp sysimgblt fb_sys_fops pps_core i2c_i801 rtsx_pci drm nvme_core psmouse ahci libahc
Jan 30 10:19:46 akaars-kubuntu kernel: CPU: 2 PID: 1158 Comm: Xorg Tainted: G OE 4.15.0-44-generic #47-Ubuntu
Jan 30 10:19:46 akaars-kubuntu kernel: Hardware name: Dell Inc. Latitude E7470/0T6HHJ, BIOS 1.6.3 06/15/2016
Jan 30 10:19:46 akaars-kubuntu kernel: RIP: 0010:intel_ddi_post_disable+0x54/0x170 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: RSP: 0018:ffffb77f82c17a60 EFLAGS: 00010297
Jan 30 10:19:46 akaars-kubuntu kernel: RAX: 0000000000000007 RBX: ffff947470358000 RCX: ffffffffc0627272
Jan 30 10:19:46 akaars-kubuntu kernel: RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff947470358000
Jan 30 10:19:46 akaars-kubuntu kernel: RBP: ffffb77f82c17a90 R08: 0000000000000001 R09: 0000000000000000
Jan 30 10:19:46 akaars-kubuntu kernel: R10: 00000000000003ef R11: 000000000000033e R12: 0000000000000000
Jan 30 10:19:46 akaars-kubuntu kernel: R13: ffff947470358000 R14: ffff94746f8d8000 R15: ffff947470b90800
Jan 30 10:19:46 akaars-kubuntu kernel: FS: 00007faeffbe7600(0000) GS:ffff94748dd00000(0000) knlGS:0000000000000000
Jan 30 10:19:46 akaars-kubuntu kernel: CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Jan 30 10:19:46 akaars-kubuntu kernel: CR2: 0000000000000245 CR3: 0000000439ba4003 CR4: 00000000003606e0
Jan 30 10:19:46 akaars-kubuntu kernel: DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Jan 30 10:19:46 akaars-kubuntu kernel: DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Jan 30 10:19:46 akaars-kubuntu kernel: Call Trace:
Jan 30 10:19:46 akaars-kubuntu kernel: ? intel_dp_sink_dpms+0xbb/0xf0 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: intel_mst_post_disable_dp+0x99/0xd0 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: intel_encoders_post_disable.isra.102+0x66/0x80 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: haswell_crtc_disable+0xe8/0x150 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: intel_atomic_commit_tail+0x7ea/0xd30 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: intel_atomic_commit+0x277/0x2b0 [i915]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_atomic_commit+0x51/0x60 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_atomic_connector_commit_dpms+0xef/0x100 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_mode_obj_set_property_ioctl+0x176/0x280 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: ? drm_mode_connector_set_obj_prop+0x80/0x80 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_mode_connector_property_set_ioctl+0x3f/0x60 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_ioctl_kernel+0x5f/0xb0 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: drm_ioctl+0x31b/0x3d0 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: ? drm_mode_connector_set_obj_prop+0x80/0x80 [drm]
Jan 30 10:19:46 akaars-kubuntu kernel: ? vfs_writev+0xb9/0x110
Jan 30 10:19:46 akaars-kubuntu kernel: do_vfs_ioctl+0xa8/0x630
Jan 30 10:19:46 akaars-kubuntu kernel: SyS_ioctl+0x79/0x90
Jan 30 10:19:46 akaars-kubuntu kernel: do_syscall_64+0x73/0x130
Jan 30 10:19:46 akaars-kubuntu kernel: entry_SYSCALL_64_after_hwframe+0x3d/0xa2
Jan 30 10:19:46 akaars-kubuntu kernel: RIP: 0033:0x7faefd00c5d7
Jan 30 10:19:46 akaars-kubuntu kernel: RSP: 002b:00007ffdd47e3eb8 EFLAGS: 00003246 ORIG_RAX: 0000000000000010
Jan 30 10:19:46 akaars-kubuntu kernel: RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007faefd00c5d7
Jan 30 10:19:46 akaars-kubuntu kernel: RDX: 00007ffdd47e3ef0 RSI: 00000000c01064ab RDI: 0000000000000018
Jan 30 10:19:46 akaars-kubuntu kernel: RBP: 00007ffdd47e3ef0 R08: 00005619bf060de0 R09: 0000000000000000
Jan 30 10:19:46 akaars-kubuntu kernel: R10: 00007ffdd47e4020 R11: 0000000000003246 R12: 00000000c01064ab
Jan 30 10:19:46 akaars-kubuntu kernel: R13: 0000000000000018 R14: 00005619beedf3f0 R15: 00005619bd7a8700
Jan 30 10:19:46 akaars-kubuntu kernel: Code: 0d f6 86 44 02 00 00 40 0f 85 81 00 00 00 83 f8 06 72 77 83 f8 08 76 13 83 f8 0a 75 6d 41 f6 86 60 06 00 00 40 0f 84 dd 00 00 00 <41> f6 84 24 45 02 00 00 08 4d 8d bd 00 01 00 00 74 3e 48 89 df
Jan 30 10:19:46 akaars-kubuntu kernel: RIP: intel_ddi_post_disable+0x54/0x170 [i915] RSP: ffffb77f82c17a60
Jan 30 10:19:46 akaars-kubuntu kernel: CR2: 0000000000000245
Jan 30 10:19:46 akaars-kubuntu kernel: ---[ end trace ba3a7dd9aa4daeca ]---
Jan 30 10:24:11 akaars-kubuntu systemd-logind[990]: Lid opened.
Jan 30 10:24:38 akaars-kubuntu systemd-logind[990]: Power key pressed.
Jan 30 10:24:43 akaars-kubuntu kernel: acpi INT3400:00: Unsupported event [0x86]
Jan 30 10:24:44 akaars-kubuntu kernel: acpi INT3400:00: Unsupported event [0x86]

[Ilya Brik (ibrik)]

Seems to be related to 1813831 and 1813543 - the same reproduction scenario.