cgroup2: \"open /sys/fs/cgroup/cgroup.subtree_control: permission denied\"": unknown.

[AkihiroSuda]

Rootless runc on cgroup v2 (but without actual cgroup control) seems to have got broken recently

$ docker --context=rootless run -it --rm alpine
docker: Error response from daemon: OCI runtime create failed: container_linux.go:348: starting container process caused "process_linux.go:305: applying cgroup configuration for process caused \"open /sys/fs/cgroup/cgroup.subtree_control: permission denied\"": unknown.
ERRO[0000] error waiting for container: context canceled 

$ docker --context=rootless info
Client:
 Debug Mode: false
 Plugins:
  buildx: Build with BuildKit (Docker Inc., v0.3.1-31-g891d355)

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 2
 Server Version: dev
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: false
 Logging Driver: json-file
 Cgroup Driver: none
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 1d083fec4939ce58f23a48ad3a914adb826d592a
 runc version: 46be7b612e2533c494e6a251111de46d8e286ed5
 init version: fec3683
 Security Options:
  seccomp
   Profile: default
  rootless
  cgroupns
 Kernel Version: 5.3.0-46-generic
 Operating System: Ubuntu 19.10
 OSType: linux
 Architecture: x86_64
 CPUs: 2
 Total Memory: 7.748GiB
 Name: suda-ws01
 ID: CWVR:KJQU:3CNT:IJF7:FMME:22Y7:GKFW:AFKJ:IVLQ:JOVW:3KZY:S25M
 Docker Root Dir: /home/suda/.local/share/docker
 Debug Mode: false
 Username: akihirosuda
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No kernel memory limit support
WARNING: No kernel memory TCP limit support

$ docker --context=rootless version
Client:
 Version:           20.03.0-dev
 API version:       1.41
 Go version:        go1.13.10
 Git commit:        abafad3df
 Built:             Tue Apr 21 15:06:56 2020
 OS/Arch:           linux/amd64
 Experimental:      true

Server:
 Engine:
  Version:          dev
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.10
  Git commit:       ba8129b28a
  Built:            Tue Apr 21 15:06:37 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v1.3.0-511-g1d083fec
  GitCommit:        1d083fec4939ce58f23a48ad3a914adb826d592a
 runc:
  Version:          1.0.0-rc10+dev
  GitCommit:        46be7b612e2533c494e6a251111de46d8e286ed5
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683

[AkihiroSuda]

Regression in 813cb3e (#2299)

[AkihiroSuda]

PR: #2340