Comment # 4 on bug 1099012 from Jiri Slaby

FWIW happens with 4.18 too:
> BUG: unable to handle kernel paging request at 000000100000005c
> PGD 0 P4D 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 4.18.4-3.gbf5cd4a-default #1 openSUSE Tumbleweed (unreleased)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
> RIP: 0010:put_css_set_locked+0x7f/0x270
> Code: ad de eb 0d 48 83 c3 10 48 83 c5 08 49 39 dd 74 52 48 8b 43 08 48 8b 13 48 89 42 08 48 89 10 4c 89 3b 4c 89 73 08 48 8b 45 00 <f6> 40 7c 01 75 d4 65 ff 05 24 50 ee 6b 48 8b 50 18 f6 c2 03 0f 85
> RSP: 0018:ffffb2fb8067fda8 EFLAGS: 00010006
> RAX: 0000000fffffffe0 RBX: ffff9172a1d470c8 RCX: 0000000000000040
> RDX: ffff9173424e6cc8 RSI: 0000000000000000 RDI: ffff9172a1d47000
> RBP: ffff9172a1d47008 R08: ffff9173401fdd20 R09: 0000000000000100
> R10: ffff9173401fd7e0 R11: ffff9173401ffd20 R12: ffff9172a1d47000
> R13: ffff9172a1d47188 R14: dead000000000200 R15: dead000000000100
> FS:  0000000000000000(0000) GS:ffff917346800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000100000005c CR3: 0000000022b98000 CR4: 00000000000006f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  cgroup_free+0x93/0xb0
>  __put_task_struct+0x3d/0x140
>  rcu_process_callbacks+0x270/0x580
>  __do_softirq+0x111/0x370
>  ? sort_range+0x20/0x20
>  run_ksoftirqd+0x30/0x40
>  smpboot_thread_fn+0xf1/0x1e0
>  kthread+0x112/0x130
>  ? kthread_create_worker_on_cpu+0x40/0x40
>  ret_from_fork+0x3a/0x50
> Modules linked in: af_packet iscsi_ibft iscsi_boot_sysfs nls_iso8859_1 nls_cp437 vfat fat snd_hda_codec_generic snd_hda_intel virtio_gpu snd_hda_codec ttm snd_hda_core snd_hwdep drm_kms_helper snd_pcm snd_timer snd ppdev drm virtio_net fb_sys_fops syscopyarea sysfillrect parport_pc sysimgblt pcspkr soundcore net_failover joydev failover virtio_balloon parport virtio_input i2c_piix4 qemu_fw_cfg button ata_generic ehci_pci uhci_hcd ehci_hcd ata_piix floppy serio_raw usbcore virtio_scsi sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua virtio_rng
> CR2: 000000100000005c
> ---[ end trace 918d9c21d8ad57cd ]---