I'm also encountering this issue, only on 19.10. My GPU is a RX 580. Tested memory for 8 hours using livecd memtest
 BUG: kernel NULL pointer dereference, address: 00000000000002ac
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0 
 Oops: 0000 [#1] SMP NOPTI
 CPU: 9 PID: 340 Comm: kworker/u64:9 Tainted: G        W  OE     5.3.0-18-generic #19-Ubuntu
 Hardware name: System manufacturer System Product Name/CROSSHAIR VI HERO, BIOS 7501 09/23/2019
 Workqueue: events_unbound commit_work [drm_kms_helper]
 RIP: 0010:dc_stream_log+0x12/0xc0 [amdgpu]
 Code: 83 f1 01 0f b6 c9 e8 8d c2 81 c7 e9 71 ff ff ff 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 f2 bf 04 00 00 00 48 89 e5 53 <8b> 86 ac 02 00 00 48 89 f3 8b 8e 0c 01 00 00 50 8b 86 28 01 00 00
 RSP: 0018:ffffc017c12d7b80 EFLAGS: 00010202
 RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000002
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
 RBP: ffffc017c12d7b88 R08: 0000000000000000 R09: 0000000000000001
 R10: ffff9efbcea573c8 R11: 0000000000000000 R12: ffff9efa9f840000
 R13: ffff9efbbae30000 R14: ffff9efa9f840000 R15: ffff9efbbad40000
 FS:  0000000000000000(0000) GS:ffff9efbcea40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00000000000002ac CR3: 00000003fe050000 CR4: 00000000003406e0
 Call Trace:
  dc_commit_state+0x7e/0xb0 [amdgpu]
  amdgpu_dm_atomic_commit_tail+0x3bf/0xfb0 [amdgpu]
  ? cpumask_next_and+0x1e/0x20
  ? free_one_page+0xb7/0x4b0
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? _cond_resched+0x19/0x30
  ? wait_for_completion_timeout+0x3a/0x120
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  ? __switch_to_asm+0x34/0x70
  ? __switch_to_asm+0x40/0x70
  commit_tail+0x41/0x70 [drm_kms_helper]
  ? commit_tail+0x41/0x70 [drm_kms_helper]
  commit_work+0x12/0x20 [drm_kms_helper]
  process_one_work+0x1db/0x380
  worker_thread+0x4d/0x400
  kthread+0x104/0x140
  ? process_one_work+0x380/0x380
  ? kthread_park+0x80/0x80
  ret_from_fork+0x22/0x40
 Modules linked in: pci_stub vboxpci(OE) vboxnetadp(OE) xfrm_user vboxnetflt(OE) xfrm4_tunnel tunnel4 ipcomp xfrm_ipcomp esp4 l2tp_ppp l2tp_netlink l2tp_core ah4 ip6_udp_tunnel vboxdrv(OE) udp_tunnel af_key xfrm_algo pppox nls_iso8859_1 snd_hda_codec_realtek snd_hda_codec_generic ledtrig_audio snd_hda_codec_hdmi snd_hda_intel snd_hda_codec snd_hda_core joydev snd_hwdep input_leds snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device snd_timer edac_mce_amd kvm_amd kvm irqbypass eeepc_wmi asus_wmi sparse_keymap video wmi_bmof snd k10temp ccp soundcore mac_hid sch_fq_codel parport_pc ppdev lp parport ip_tables x_tables autofs4 dm_crypt hid_generic usbhid hid amdgpu crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel amd_iommu_v2 gpu_sched ttm aes_x86_64 crypto_simd drm_kms_helper syscopyarea cryptd sysfillrect glue_helper sysimgblt fb_sys_fops mxm_wmi drm igb i2c_piix4 nvme dca ahci nvme_core i2c_algo_bit libahci gpio_amdpt wmi gpio_generic
 CR2: 00000000000002ac
 ---[ end trace 57ff7a836204c53a ]---
 RIP: 0010:dc_stream_log+0x12/0xc0 [amdgpu]
 Code: 83 f1 01 0f b6 c9 e8 8d c2 81 c7 e9 71 ff ff ff 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 f2 bf 04 00 00 00 48 89 e5 53 <8b> 86 ac 02 00 00 48 89 f3 8b 8e 0c 01 00 00 50 8b 86 28 01 00 00
 RSP: 0018:ffffc017c12d7b80 EFLAGS: 00010202
 RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000002
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
 RBP: ffffc017c12d7b88 R08: 0000000000000000 R09: 0000000000000001
 R10: ffff9efbcea573c8 R11: 0000000000000000 R12: ffff9efa9f840000
 R13: ffff9efbbae30000 R14: ffff9efa9f840000 R15: ffff9efbbad40000
 FS:  0000000000000000(0000) GS:ffff9efbcea40000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00000000000002ac CR3: 00000003fe050000 CR4: 00000000003406e0