ChromeOS builders can't always clean up loopback devices after themselves, because of umount kernel bugs. So, we are supposed to reboot between builds to ensure things are clean for the next build.

That does not always appear to be happening, which can kill builds at startup in confusing ways.


https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/buildDetails?buildbucketId=8932745453427979040

cbuildbot_launch: Unhandled exception:
Traceback (most recent call last):
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch", line 169, in <module>
    DoMain()
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch", line 165, in DoMain
    commandline.ScriptWrapperMain(FindTarget)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/lib/commandline.py", line 912, in ScriptWrapperMain
    ret = target(argv[1:])
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch.py", line 497, in main
    return _main(argv)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch.py", line 464, in _main
    CleanBuildRoot(root, repo, metrics_fields, build_state)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch.py", line 72, in wrapped_functor
    result = functor(*args, **kwargs)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/scripts/cbuildbot_launch.py", line 260, in CleanBuildRoot
    osutils.RmDir(root, ignore_missing=True, sudo=True)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/lib/osutils.py", line 394, in RmDir
    redirect_stdout=True, redirect_stderr=True)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/lib/cros_build_lib.py", line 322, in SudoRunCommand
    return RunCommand(sudo_cmd, **kwargs)
  File "/b/swarming/w/ir/kitchen-workdir/chromite/lib/cros_build_lib.py", line 647, in RunCommand
    raise RunCommandError(msg, cmd_result)
chromite.lib.cros_build_lib.RunCommandError: return code: 1; command: sudo -- rm -rf -- /b/swarming/w/ir/cache/cbuild
rm: cannot remove &#8216;/b/swarming/w/ir/cache/cbuild/repository/new-sdk-chroot&#8217;: Device or resource busy
cmd=['sudo', '--', 'rm', '-rf', '--', '/b/swarming/w/ir/cache/cbuild']