[Navi] drm_WARN_ON(atomic_read(&vblank->refcount) == 0)

RX 5600 XT, Linux 5.9.8. 2 monitors (one DP, one HDMI). Only DP appears to be affected.

I removed power from the monitor. This caused an error:

drm:retrieve_link_cap] *ERROR* retrieve_link_cap: Read dpcd data failed.

I then restored power and forced the display to be blanked. This triggered the following warning:

amdgpu 0000:28:00.0: drm_WARN_ON(atomic_read(&vblank->refcount) == 0)
WARNING: CPU: 3 PID: 0 at drm_vblank_put+0xa2/0xf0
Modules linked in: cmac cpufreq_conservative bnep efivarfs vfat fat nct6775 hwmon_vid em28xx_rc tda18271 cxd2820r regmap_i2c si2157 si2168 i2c_mux em28xx_dvb pktcdvd btusb btbcm btintel bluetooth uvcvideo ecdh_generic videobuf2_vmalloc ecc videobuf2_memops videobuf2_v4l2 em28xx snd_usb_audio videobuf2_common joydev snd_usbmidi_lib tveeprom snd_hda_codec_realtek snd_hwdep snd_rawmidi snd_hda_codec_generic snd_seq_device snd_hda_codec_hdmi ledtrig_audio snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hda_core snd_pcm_oss snd_mixer_oss snd_pcm snd_timer sp5100_tco k10temp sg
CPU: 3 PID: 0 Comm: swapper/3 Tainted: G        W         5.9.8 #1
Hardware name: Micro-Star International Co., Ltd MS-7C02/B450 TOMAHAWK MAX (MS-7C02), BIOS 3.70 06/09/2020
RIP: 0010:drm_vblank_put+0xa2/0xf0
Code: 48 8b 5f 50 48 85 db 75 03 48 8b 1f e8 17 8c 33 00 48 c7 c1 60 53 7e 82 48 89 da 48 c7 c7 50 d9 7d 82 48 89 c6 e8 d7 71 5d 00 <0f> 0b 5b c3 48 8d 79 20 5b e9 e0 fd ff ff 48 8b 7f 18 48 8b 5f 50
RSP: 0018:ffffc900001a8e10 EFLAGS: 00210082
RAX: 0000000000000000 RBX: ffff88840c5f31e0 RCX: 0000000000010004
RDX: 0000000080010004 RSI: ffffffff82fa4e25 RDI: 00000000ffffffff
RBP: ffff88840b300000 R08: ffffffff82fa4de0 R09: 000000000001bb40
R10: 000120fcba1e9924 R11: 0000000080000003 R12: 0000000000200086
R13: 0000000000000000 R14: ffff8883da566500 R15: ffff88840b314948
FS:  0000000000000000(0000) GS:ffff88840ecc0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe36078900c CR3: 00000003aacdc000 CR4: 0000000000350ee0
Call Trace:
 <IRQ>
 dm_pflip_high_irq+0xb6/0x260
 amdgpu_dm_irq_handler+0x75/0x110
 amdgpu_irq_dispatch+0x96/0x140
 amdgpu_ih_process+0x89/0x110
 amdgpu_irq_handler+0x1a/0x90
 __handle_irq_event_percpu+0x2e/0xc0
 ? handle_level_irq+0x130/0x130
 handle_irq_event_percpu+0x2b/0x70
 handle_irq_event+0x2f/0x50
 ? handle_level_irq+0x130/0x130
 handle_edge_irq+0xa3/0x1a0
 asm_call_irq_on_stack+0x12/0x20
 </IRQ>
 common_interrupt+0x118/0x1b0
 asm_common_interrupt+0x1e/0x40
RIP: 0010:cpuidle_enter_state+0xb8/0x2a0
Code: e8 ed f1 7c ff 31 ff 48 89 c5 e8 a3 06 7d ff 45 84 ff 74 12 9c 58 f6 c4 02 0f 85 a3 01 00 00 31 ff e8 6c 25 81 ff fb 45 85 f6 <0f> 88 b0 00 00 00 49 63 c6 48 29 dd 48 8d 14 40 48 8d 14 90 49 8d
RSP: 0018:ffffc900000bbeb0 EFLAGS: 00200202
RAX: ffff88840ecc0000 RBX: 0000502c6ffee068 RCX: 000000000000001f
RDX: 0000502c703d5b5e RSI: ffffffff827b283b RDI: ffffffff827c57de
RBP: 0000502c703d5b5e R08: 0000000000000002 R09: 000000000001bb40
R10: 000120fcba1c4160 R11: ffff88840ecdb444 R12: ffffffff82a4b740
R13: ffff88840cace000 R14: 0000000000000002 R15: 0000000000000000
 cpuidle_enter+0x24/0x40
 do_idle+0x1b6/0x1f0
 cpu_startup_entry+0x14/0x20
 secondary_startup_64+0xa4/0xb0