Comment 1 for bug 1918668

One other example:

[ 41.499636] BUG: kernel NULL pointer dereference, address: 0000000000000518
[ 41.506015] #PF: supervisor read access in kernel mode
[ 41.508850] #PF: error_code(0x0000) - not-present page
[ 41.510728] PGD 0 P4D 0
[ 41.511714] Oops: 0000 [#1] SMP PTI
[ 41.513040] CPU: 1 PID: 198 Comm: kworker/u8:4 Tainted: G W 5.8.0-45-generic #51
[ 41.516172] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-1 04/01/2014
[ 41.519019] Workqueue: writeback wb_workfn (flush-252:0)
[ 41.520954] RIP: 0010:__mod_memcg_state.part.0+0xc/0x90
[ 41.522845] Code: f0 56 30 93 e8 15 9f 2e 00 5b 41 5c 41 5d 5d c3 4c 8b 25 ff 52 99 01 e9 76 ff ff ff 0f 0b 0f 1f 44 00 00 48 63 d2 55 48 63 f6 <48> 8b 87 18 05 00 00 65 48 8b 0c f0 48 01 ca 48 c1 e6 03 49 89 d0
[ 41.536800] RSP: 0018:ffffabad803ff7d8 EFLAGS: 00010097
[ 41.540726] RAX: ffffffffffffffe2 RBX: 0000000000000011 RCX: 0000000000032192
[ 41.543210] RDX: ffffffffffffffff RSI: 0000000000000011 RDI: 0000000000000000
[ 41.545567] RBP: ffffabad803ff810 R08: ffffffffffffffff R09: ffff96e43801ec00
[ 41.547992] R10: 0000000000000000 R11: 0000000000001000 R12: ffff96e43801ec00
[ 41.550528] R13: ffffffffffffffff R14: 0000000000000000 R15: ffff96e43ffb2000
[ 41.552904] FS: 0000000000000000(0000) GS:ffff96e43dc80000(0000) knlGS:0000000000000000
[ 41.557020] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 41.559173] CR2: 0000000000000518 CR3: 0000000035f4c000 CR4: 00000000000006e0
[ 41.561005] Call Trace:
[ 41.561769] ? __mod_lruvec_state+0x47/0xf0
[ 41.562897] clear_page_dirty_for_io+0x187/0x200
[ 41.564111] mpage_submit_page+0x24/0x90
[ 41.565181] mpage_map_and_submit_buffers+0xe3/0x190
[ 41.566477] mpage_map_and_submit_extent+0x5a/0x200
[ 41.567732] ext4_writepages+0x671/0x860
[ 41.568882] ? update_load_avg+0x82/0x630
[ 41.570181] do_writepages+0x38/0xc0
[ 41.571320] ? write_inode+0x5c/0x100
[ 41.572625] __writeback_single_inode+0x40/0x230
[ 41.574046] writeback_sb_inodes+0x22a/0x4e0
[ 41.575380] __writeback_inodes_wb+0x56/0xf0
[ 41.576798] wb_writeback+0x201/0x2e0
[ 41.578252] wb_check_old_data_flush+0xb7/0xc0
[ 41.580364] wb_do_writeback+0xbe/0x180
[ 41.581989] ? set_worker_desc+0xa6/0xb0
[ 41.583553] wb_workfn+0x74/0x290
[ 41.589094] ? __switch_to+0x7f/0x380
[ 41.590524] ? __switch_to_asm+0x42/0x70
[ 41.591753] ? __switch_to_asm+0x36/0x70
[ 41.593102] process_one_work+0x1e8/0x3b0
[ 41.594571] worker_thread+0x50/0x370
[ 41.595935] kthread+0x12f/0x150
[ 41.597224] ? process_one_work+0x3b0/0x3b0
[ 41.598772] ? __kthread_bind_mask+0x70/0x70
[ 41.600473] ret_from_fork+0x22/0x30
[ 41.601997] Modules linked in: isofs binfmt_misc nls_iso8859_1 input_leds joydev serio_raw sch_fq_codel drm ip_tables x_tables autofs4 ahci xhci_pci xhci_pci_renesas psmouse virtio_net libahci net_failover virtio_blk failover
[ 41.609197] CR2: 0000000000000518
[ 41.610567] ---[ end trace 63fecb49c24b6bde ]---
[ 41.612023] RIP: 0010:__mod_memcg_state.part.0+0xc/0x90
[ 41.613631] Code: f0 56 30 93 e8 15 9f 2e 00 5b 41 5c 41 5d 5d c3 4c 8b 25 ff 52 99 01 e9 76 ff ff ff 0f 0b 0f 1f 44 00 00 48 63 d2 55 48 63 f6 <48> 8b 87 18 05 00 00 65 48 8b 0c f0 48 01 ca 48 c1 e6 03 49 89 d0
[ 41.623236] RSP: 0018:ffffabad803ff7d8 EFLAGS: 00010097
[ 41.625530] RAX: ffffffffffffffe2 RBX: 0000000000000011 RCX: 0000000000032192
[ 41.629038] RDX: ffffffffffffffff RSI: 0000000000000011 RDI: 0000000000000000
[ 41.632316] RBP: ffffabad803ff810 R08: ffffffffffffffff R09: ffff96e43801ec00
[ 41.635007] R10: 0000000000000000 R11: 0000000000001000 R12: ffff96e43801ec00
[ 41.637663] R13: ffffffffffffffff R14: 0000000000000000 R15: ffff96e43ffb2000
[ 41.640305] FS: 0000000000000000(0000) GS:ffff96e43dc80000(0000) knlGS:0000000000000000
[ 41.643404] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 41.645522] CR2: 0000000000000518 CR3: 0000000035f4c000 CR4: 00000000000006e0
[ 41.647610] ------------[ cut here ]------------