GPU hang when waking up VR headset (SteamVR, compositing, VRR)

(This is a copy of SteamVR bug 519.)

A GPU hang will occur when the headset display is activated (i.e. vrcompositor becomes active) if VRR is in use. I have only tested with xfwm4 with compositing enabled.

(I'm not certain whether this qualifies as a vrcompositor bug, an xfwm4 bug, a kernel bug or some combination of these.)

To reproduce

• Whitelist xfwm4 for VRR. The following ~/.drirc is sufficient:

<driconf>
  <device screen="0" driver="radeonsi">
    <application name="xfwm4" executable="xfwm4">
      <option name="adaptive_sync" value="true" />
    </application>
  </device>
</driconf>

• Restart xfwm4 (xfwm4 --replace & disown).
• Start SteamVR.
• Move the headset.

At this point, there will be a GPU hang. GPU reset should succeed, but X will need to be restarted.

System information

• Distribution: Devuan chimaera (with libdrm & libvulkan packages from daedalus)
• SteamVR version: 1.22.12
• Steam client version: 1653101165
• Opted into Steam client beta?: Yes
• Graphics driver version: Mesa 22.1.0 (local build derived from Debian experimental)
• GPU: Radeon RX 5600 XT
• Kernel version: 5.17.4 (local build)
• Displays attached: 1080p 144Hz Freesync (primary); 1080p 60Hz; Vive (original).
• SteamVR async reprojection: enabled

Additional context

Kernel log text extract

X config note: xf86-video-amdgpu 22.0 is in use; VariableRefresh & AsyncFlipSecondaries are enabled.