Comment 2 for bug 1862114

dmesg output on focal:
[ 951.293174] LTP: starting pty03
[ 951.305037] SLIP: version 0.8.4-NET3.019-NEWTTY (dynamic channels, max=256) (6 bit encapsulation enabled).
[ 951.305038] CSLIP: code copyright 1989 Regents of the University of California.
[ 951.305039] SLIP linefill/keepalive option.
[ 951.306823] BUG: kernel NULL pointer dereference, address: 0000000000000020
[ 951.309960] #PF: supervisor write access in kernel mode
[ 951.312130] #PF: error_code(0x0002) - not-present page
[ 951.314227] PGD 0 P4D 0
[ 951.315278] Oops: 0002 [#1] SMP PTI
[ 951.316705] CPU: 1 PID: 39102 Comm: pty03 Not tainted 5.4.0-12-generic #15-Ubuntu
[ 951.319737] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 951.322713] RIP: 0010:queue_work_on+0x1b/0x50
[ 951.324175] Code: 75 01 01 e8 b2 05 fe ff 0f 0b e9 c3 fc ff ff 0f 1f 44 00 00 55 48 89 e5 53 9c 58 0f 1f 44 00 00 48 89 c3 fa 66 0f 1f 44 00 00 <f0> 48 0f ba 2a 00 73 13 45 31 c0 48 89 df 57 9d 0f 1f 44 00 00 44
[ 951.329576] RSP: 0018:ffffab9380557cb8 EFLAGS: 00010002
[ 951.331197] RAX: 0000000000000202 RBX: 0000000000000202 RCX: 0000000000000000
[ 951.333358] RDX: 0000000000000020 RSI: ffff8c65fb00ae00 RDI: 0000000000002000
[ 951.335566] RBP: ffffab9380557cc0 R08: 0000000000000001 R09: 0000000000000006
[ 951.337743] R10: ffff8c65f8f4cb00 R11: 0000000000000000 R12: ffff8c65ea61f550
[ 951.339955] R13: 0000000000000000 R14: ffff8c65eda51400 R15: ffff8c65f9002a00
[ 951.342084] FS: 00007f808362a700(0000) GS:ffff8c65fbb00000(0000) knlGS:0000000000000000
[ 951.344442] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 951.346163] CR2: 0000000000000020 CR3: 000000012a64c000 CR4: 00000000000006e0
[ 951.348264] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 951.350422] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 951.352494] Call Trace:
[ 951.353244] slip_write_wakeup+0x25/0x30 [slip]
[ 951.354600] tty_wakeup+0x5b/0x70
[ 951.355539] pty_unthrottle+0x19/0x30
[ 951.356560] tty_unthrottle+0x42/0x60
[ 951.357566] __tty_perform_flush+0x87/0x90
[ 951.358768] n_tty_ioctl_helper+0xcc/0x150
[ 951.359955] n_tty_ioctl+0x2d/0x100
[ 951.360930] tty_ioctl+0x3c0/0x8e0
[ 951.361882] ? __switch_to_asm+0x34/0x70
[ 951.363049] ? __switch_to_asm+0x40/0x70
[ 951.364191] ? __switch_to_asm+0x34/0x70
[ 951.365261] ? __switch_to_asm+0x40/0x70
[ 951.366382] ? __switch_to_asm+0x34/0x70
[ 951.367452] ? __switch_to_asm+0x40/0x70
[ 951.368523] ? __switch_to_asm+0x34/0x70
[ 951.369693] ? __switch_to_asm+0x40/0x70
[ 951.370829] ? __switch_to_asm+0x34/0x70
[ 951.371923] ? __switch_to_asm+0x40/0x70
[ 951.372998] ? __switch_to_asm+0x34/0x70
[ 951.374097] ? __switch_to_asm+0x40/0x70
[ 951.375183] ? __switch_to_asm+0x34/0x70
[ 951.376288] ? __switch_to_asm+0x40/0x70
[ 951.377390] ? __switch_to+0x110/0x470
[ 951.378863] do_vfs_ioctl+0x407/0x670
[ 951.380269] ? __schedule+0x2eb/0x740
[ 951.381761] ksys_ioctl+0x67/0x90
[ 951.383076] __x64_sys_ioctl+0x1a/0x20
[ 951.384510] do_syscall_64+0x57/0x190
[ 951.385896] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 951.387655] RIP: 0033:0x7f808374568b
[ 951.389147] Code: 0f 1e fa 48 8b 05 05 28 0d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d5 27 0d 00 f7 d8 64 89 01 48
[ 951.395021] RSP: 002b:00007f8083629ec8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[ 951.397467] RAX: ffffffffffffffda RBX: 000000000000000a RCX: 00007f808374568b
[ 951.399824] RDX: 0000000000000000 RSI: 000000000000540b RDI: 0000000000000006
[ 951.402105] RBP: 00005627b8f404c6 R08: 00007ffee1d0c1b0 R09: 00005627b8f4b320
[ 951.404415] R10: 00005627b8f4b318 R11: 0000000000000246 R12: 0000000000000000
[ 951.406754] R13: 00007ffee1c03cbf R14: 00007ffee1c03cc0 R15: 00007f8083629fc0
[ 951.409192] Modules linked in: slip serport dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua kvm_intel joydev kvm input_leds serio_raw mac_hid qemu_fw_cfg sch_fq_codel ip_tables x_tables autofs4 btrfs zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear cirrus drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm virtio_net net_failover failover virtio_blk psmouse i2c_piix4 pata_acpi floppy
[ 951.424165] CR2: 0000000000000020
[ 951.425788] ---[ end trace 41434fc402e37fd0 ]---
[ 951.427905] RIP: 0010:queue_work_on+0x1b/0x50
[ 951.429933] Code: 75 01 01 e8 b2 05 fe ff 0f 0b e9 c3 fc ff ff 0f 1f 44 00 00 55 48 89 e5 53 9c 58 0f 1f 44 00 00 48 89 c3 fa 66 0f 1f 44 00 00 <f0> 48 0f ba 2a 00 73 13 45 31 c0 48 89 df 57 9d 0f 1f 44 00 00 44
[ 951.437519] RSP: 0018:ffffab9380557cb8 EFLAGS: 00010002
[ 951.439860] RAX: 0000000000000202 RBX: 0000000000000202 RCX: 0000000000000000
[ 951.442897] RDX: 0000000000000020 RSI: ffff8c65fb00ae00 RDI: 0000000000002000
[ 951.445937] RBP: ffffab9380557cc0 R08: 0000000000000001 R09: 0000000000000006
[ 951.449000] R10: ffff8c65f8f4cb00 R11: 0000000000000000 R12: ffff8c65ea61f550
[ 951.451758] R13: 0000000000000000 R14: ffff8c65eda51400 R15: ffff8c65f9002a00
[ 951.454521] FS: 00007f808362a700(0000) GS:ffff8c65fbb00000(0000) knlGS:0000000000000000
[ 951.457385] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 951.459435] CR2: 0000000000000020 CR3: 000000012a64c000 CR4: 00000000000006e0
[ 951.461819] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 951.464248] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400