OpenJDK 17.0.2 - Cgroup v1 initialization causes NullPointerException when cgroup path does not start with the mount root

An_Issue_description.md

When I ran wildfly testsuite on JDK 17 within a podman container, I got NPE for all tests, please refer to NPE.stacktrace.java below on the stack trace, all work fine if I run it on base metal.

It relates to JDK issue: https://bugs.openjdk.java.net/browse/JDK-8272124, but this demostrates another case when the cgroup path does not start with the mount root.

In this case /proc/self/cgroup has the following line:

9:memory:/user.slice/user-1000.slice/session-3.scope

while /proc/self/mountinfo has the following line:

941 931 0:36 /user.slice/user-1000.slice/session-50.scope /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,memory

The environment:

• Java version

openjdk version "17.0.2" 2022-01-18
OpenJDK Runtime Environment 21.9 (build 17.0.2+8)
OpenJDK 64-Bit Server VM 21.9 (build 17.0.2+8, mixed mode, sharing)

• RHEL 8.5:

[jenkins@testjenkins ~]$ uname -a
Linux testjenkins 4.18.0-348.el8.x86_64 #1 SMP Mon Oct 4 12:17:22 EDT 2021 x86_64 x86_64 x86_64 GNU/Linux
[jenkins@testjenkins ~]$ cat /etc/redhat-release 
Red Hat Enterprise Linux release 8.5 (Ootpa)

• podman version:

[jenkins@testjenkins ~]$ podman --version
podman version 3.4.2

• podman container inspection Please refer to the podman_container_inspect.json file below.

• The /proc/self/mountinfo within the container Please refer to the proc_self_mountinfo file below

• The /proc/self/cgroup within the container Please refer to the proc_self_cgroup file below

• The /proc/cgroups within the container Please refer to the proc_cgroups file below

• The reproducer Please see the reproducer: Z_cgroup_v1_npe_when_cgrouppath_does_not_start_with_mount_root.patch

NPE.stacktrace.java

```
[ERROR] Failed to execute goal org.wildfly.plugins:wildfly-maven-plugin:2.0.1.Final:execute-commands (apply-elytron) on project wildfly-ts-integ-smoke: Failed to execute commands: Exception in thread "main"
 java.lang.NullPointerException
[ERROR]         at java.base/java.util.Objects.requireNonNull(Objects.java:208)
[ERROR]         at java.base/sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:263)
[ERROR]         at java.base/java.nio.file.Path.of(Path.java:147)
[ERROR]         at java.base/java.nio.file.Paths.get(Paths.java:69)
[ERROR]         at java.base/jdk.internal.platform.CgroupUtil.lambda$readStringValue$1(CgroupUtil.java:67)
[ERROR]         at java.base/java.security.AccessController.doPrivileged(AccessController.java:569)
[ERROR]         at java.base/jdk.internal.platform.CgroupUtil.readStringValue(CgroupUtil.java:69)
[ERROR]         at java.base/jdk.internal.platform.CgroupSubsystemController.getStringValue(CgroupSubsystemController.java:65)
[ERROR]         at java.base/jdk.internal.platform.CgroupSubsystemController.getLongValue(CgroupSubsystemController.java:124)
[ERROR]         at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getLongValue(CgroupV1Subsystem.java:175)
[ERROR]         at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getHierarchical(CgroupV1Subsystem.java:149)
[ERROR]         at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.initSubSystem(CgroupV1Subsystem.java:84)
[ERROR]         at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getInstance(CgroupV1Subsystem.java:60)
[ERROR]         at java.base/jdk.internal.platform.CgroupSubsystemFactory.create(CgroupSubsystemFactory.java:116)
[ERROR]         at java.base/jdk.internal.platform.CgroupMetrics.getInstance(CgroupMetrics.java:167)
[ERROR]         at java.base/jdk.internal.platform.SystemMetrics.instance(SystemMetrics.java:29)
[ERROR]         at java.base/jdk.internal.platform.Metrics.systemMetrics(Metrics.java:58)
[ERROR]         at java.base/jdk.internal.platform.Container.metrics(Container.java:43)
[ERROR]         at jdk.management/com.sun.management.internal.OperatingSystemImpl.<init>(OperatingSystemImpl.java:182)
[ERROR]         at jdk.management/com.sun.management.internal.PlatformMBeanProviderImpl.getOperatingSystemMXBean(PlatformMBeanProviderImpl.java:280)
[ERROR]         at jdk.management/com.sun.management.internal.PlatformMBeanProviderImpl$3.nameToMBeanMap(PlatformMBeanProviderImpl.java:199)
[ERROR]         at java.management/java.lang.management.ManagementFactory.lambda$getPlatformMBeanServer$0(ManagementFactory.java:488)
[ERROR]         at java.base/java.util.stream.ReferencePipeline$7$1.accept(ReferencePipeline.java:273)
[ERROR]         at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
[ERROR]         at java.base/java.util.HashMap$ValueSpliterator.forEachRemaining(HashMap.java:1779)
[ERROR]         at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
[ERROR]         at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
[ERROR]         at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
[ERROR]         at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
[ERROR]         at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
[ERROR]         at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
[ERROR]         at java.management/java.lang.management.ManagementFactory.getPlatformMBeanServer(ManagementFactory.java:489)
[ERROR]         at org.jboss.modules.ModuleLoader$RealMBeanReg$1.run(ModuleLoader.java:1258)
[ERROR]         at org.jboss.modules.ModuleLoader$RealMBeanReg$1.run(ModuleLoader.java:1256)
[ERROR]         at java.base/java.security.AccessController.doPrivileged(AccessController.java:318)
[ERROR]         at org.jboss.modules.ModuleLoader$RealMBeanReg.<init>(ModuleLoader.java:1256)
[ERROR]         at org.jboss.modules.ModuleLoader$TempMBeanReg.installReal(ModuleLoader.java:1240)
[ERROR]         at org.jboss.modules.ModuleLoader.installMBeanServer(ModuleLoader.java:273)
[ERROR]         at org.jboss.modules.Main.main(Main.java:605)
```

podman_container_inspect.json

[
    {
        "Id": "1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac",
        "Created": "2022-05-02T20:48:21.078644068+08:00",
        "Path": "/var/jenkins_home/workspace/eap-7.4.x-testsuite/hera/wait.sh",
        "Args": [
            "/var/jenkins_home/workspace/eap-7.4.x-testsuite/hera/wait.sh"
        ],
        "State": {
            "OciVersion": "1.0.2-dev",
            "Status": "running",
            "Running": true,
            "Paused": false,
            "Restarting": false,
            "OOMKilled": false,
            "Dead": false,
            "Pid": 7632,
            "ConmonPid": 7619,
            "ExitCode": 0,
            "Error": "",
            "StartedAt": "2022-05-02T20:48:21.288271319+08:00",
            "FinishedAt": "0001-01-01T00:00:00Z",
            "Healthcheck": {
                "Status": "",
                "FailingStreak": 0,
                "Log": null
            }
        },
        "Image": "bfebb38e834973abcdd7928c858b36c7b1f2540f409ce440671bb6237bdbe03f",
        "ImageName": "localhost/automatons:latest",
        "Rootfs": "",
        "Pod": "",
        "ResolvConfPath": "/run/user/1000/containers/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/resolv.conf",
        "HostnamePath": "/run/user/1000/containers/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/hostname",
        "HostsPath": "/run/user/1000/containers/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/hosts",
        "StaticDir": "/home/jenkins/.local/share/containers/storage/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata",
        "OCIConfigPath": "/home/jenkins/.local/share/containers/storage/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/config.json",
        "OCIRuntime": "runc",
        "ConmonPidFile": "/run/user/1000/containers/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/conmon.pid",
        "PidFile": "/run/user/1000/containers/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/pidfile",
        "Name": "automaton-slave-eap-7.4.x-testsuite-19",
        "RestartCount": 0,
        "Driver": "overlay",
        "MountLabel": "system_u:object_r:container_file_t:s0:c334,c907",
        "ProcessLabel": "system_u:system_r:container_t:s0:c334,c907",
        "AppArmorProfile": "",
        "EffectiveCaps": null,
        "BoundingCaps": [
            "CAP_CHOWN",
            "CAP_DAC_OVERRIDE",
            "CAP_FOWNER",
            "CAP_FSETID",
            "CAP_KILL",
            "CAP_NET_BIND_SERVICE",
            "CAP_NET_RAW",
            "CAP_SETFCAP",
            "CAP_SETGID",
            "CAP_SETPCAP",
            "CAP_SETUID",
            "CAP_SYS_CHROOT"
        ],
        "ExecIDs": [
            "cd38093eb72bc4947e6a09a297cd767ec49ef26cac452b2839d7c47713cb0de6"
        ],
        "GraphDriver": {
            "Name": "overlay",
            "Data": {
                "LowerDir": "/home/jenkins/.local/share/containers/storage/overlay/904c65c233abd3aa8ecbe08a1f3d6a4a4a7704abe47e673ffcea9030d082a9b8/diff:/home/jenkins/.local/share/containers/storage/overlay/930a368523e8d9ca054beac02aa2ec0009395486ab58c5a9d7646102e7a33601/diff:/home/jenkins/.local/share/containers/storage/overlay/ee494184ff635908355ff3828a5fdb21dae83f453bac2cdd4f147b315fbb75d2/diff:/home/jenkins/.local/share/containers/storage/overlay/1e4f5e9e1e495a879ebbb6c9c406a3b77016d74024d2d8ebdc4a56ee7434a580/diff:/home/jenkins/.local/share/containers/storage/overlay/5370b65977de2ed522b13ebaeca0fd41501f6eab2c55513c5d927594c2c253e4/diff:/home/jenkins/.local/share/containers/storage/overlay/93749af418e72b7f9d1998cdf41d4007dc27065fe4d79a3a05abf4bf274a2fac/diff",
                "MergedDir": "/home/jenkins/.local/share/containers/storage/overlay/5f2f3e72dd86114d232fed1d07a450bcb60c84c3d55123ed797c82941a8eb9a6/merged",
                "UpperDir": "/home/jenkins/.local/share/containers/storage/overlay/5f2f3e72dd86114d232fed1d07a450bcb60c84c3d55123ed797c82941a8eb9a6/diff",
                "WorkDir": "/home/jenkins/.local/share/containers/storage/overlay/5f2f3e72dd86114d232fed1d07a450bcb60c84c3d55123ed797c82941a8eb9a6/work"
            }
        },
        "Mounts": [
            {
                "Type": "bind",
                "Source": "/opt",
                "Destination": "/opt",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/.m2",
                "Destination": "/var/jenkins_home/.m2/",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": true,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/.ssh",
                "Destination": "/var/jenkins_home/.ssh/",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/.gitconfig",
                "Destination": "/var/jenkins_home/.gitconfig",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/.netrc",
                "Destination": "/var/jenkins_home/.netrc",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/current/jobs/eap-7.4.x-build/builds/7/archive",
                "Destination": "/parent_job/",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "bind",
                "Source": "/home/jenkins/current/workspace/eap-7.4.x-testsuite",
                "Destination": "/var/jenkins_home/workspace/eap-7.4.x-testsuite",
                "Driver": "",
                "Mode": "",
                "Options": [
                    "rbind"
                ],
                "RW": true,
                "Propagation": "rprivate"
            }
        ],
        "Dependencies": [],
        "NetworkSettings": {
            "EndpointID": "",
            "Gateway": "",
            "IPAddress": "",
            "IPPrefixLen": 0,
            "IPv6Gateway": "",
            "GlobalIPv6Address": "",
            "GlobalIPv6PrefixLen": 0,
            "MacAddress": "",
            "Bridge": "",
            "SandboxID": "",
            "HairpinMode": false,
            "LinkLocalIPv6Address": "",
            "LinkLocalIPv6PrefixLen": 0,
            "Ports": {},
            "SandboxKey": ""
        },
        "ExitCommand": [
            "/usr/bin/podman",
            "--root",
            "/home/jenkins/.local/share/containers/storage",
            "--runroot",
            "/run/user/1000/containers",
            "--log-level",
            "warning",
            "--cgroup-manager",
            "cgroupfs",
            "--tmpdir",
            "/run/user/1000/libpod/tmp",
            "--runtime",
            "runc",
            "--storage-driver",
            "overlay",
            "--events-backend",
            "file",
            "container",
            "cleanup",
            "--rm",
            "1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac"
        ],
        "Namespace": "",
        "IsInfra": false,
        "Config": {
            "Hostname": "1a2b19d89150",
            "Domainname": "",
            "User": "1000:1000",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
                "TERM=xterm",
                "container=oci",
                "HOME=/var/jenkins_home/",
                "HOSTNAME=1a2b19d89150"
            ],
            "Cmd": [
                "/var/jenkins_home/workspace/eap-7.4.x-testsuite/hera/wait.sh"
            ],
            "Image": "localhost/automatons:latest",
            "Volumes": null,
            "WorkingDir": "/var/jenkins_home/workspace/eap-7.4.x-testsuite",
            "Entrypoint": "",
            "OnBuild": null,
            "Labels": {
                "architecture": "x86_64",
                "build-date": "2022-03-16T16:53:14.681638",
                "com.redhat.build-host": "cpt-1001.osbs.prod.upshift.rdu2.redhat.com",
                "com.redhat.component": "ubi8-container",
                "com.redhat.license_terms": "https://www.redhat.com/en/about/red-hat-end-user-license-agreements#UBI",
                "description": "The Universal Base Image is designed and engineered to be the base layer for all of your containerized applications, middleware and utilities. This base image is freely redistributable, but Red Hat only supports Red Hat technologies through subscriptions for Red Hat products. This image is maintained by Red Hat and updated regularly.",
                "distribution-scope": "public",
                "io.buildah.version": "1.23.1",
                "io.k8s.description": "The Universal Base Image is designed and engineered to be the base layer for all of your containerized applications, middleware and utilities. This base image is freely redistributable, but Red Hat only supports Red Hat technologies through subscriptions for Red Hat products. This image is maintained by Red Hat and updated regularly.",
                "io.k8s.display-name": "Red Hat Universal Base Image 8",
                "io.openshift.expose-services": "",
                "io.openshift.tags": "base rhel8",
                "maintainer": "Red Hat, Inc.",
                "name": "ubi8",
                "release": "236.1647448331",
                "summary": "Provides the latest release of Red Hat Universal Base Image 8.",
                "url": "https://access.redhat.com/containers/#/registry.access.redhat.com/ubi8/images/8.5-236.1647448331",
                "vcs-ref": "3aadd00326f3dd6cfe65ee31017ab98915fddb56",
                "vcs-type": "git",
                "vendor": "Red Hat, Inc.",
                "version": "8.5"
            },
            "Annotations": {
                "io.container.manager": "libpod",
                "io.kubernetes.cri-o.Created": "2022-05-02T20:48:21.078644068+08:00",
                "io.kubernetes.cri-o.TTY": "false",
                "io.podman.annotations.autoremove": "TRUE",
                "io.podman.annotations.init": "FALSE",
                "io.podman.annotations.privileged": "FALSE",
                "io.podman.annotations.publish-all": "FALSE",
                "org.opencontainers.image.base.digest": "sha256:e2cbaf307f898bb43ad5e0b67bd9325c585d5e1890de0dfe7d4832d634abd39e",
                "org.opencontainers.image.base.name": "registry.access.redhat.com/ubi8/ubi:latest",
                "org.opencontainers.image.stopSignal": "15"
            },
            "StopSignal": 15,
            "CreateCommand": [
                "podman",
                "run",
                "--name",
                "automaton-slave-eap-7.4.x-testsuite-19",
                "--userns=keep-id",
                "-u",
                "1000:1000",
                "--add-host=olympus:10.88.0.1",
                "--rm",
                "-v",
                "/home/jenkins/current//jobs/eap-7.4.x-build/builds/7/archive:/parent_job/:ro",
                "--workdir",
                "/var/jenkins_home/workspace/eap-7.4.x-testsuite",
                "-v",
                "/home/jenkins/current/workspace/eap-7.4.x-testsuite:/var/jenkins_home/workspace/eap-7.4.x-testsuite:rw",
                "-v",
                "/opt:/opt:ro",
                "-v",
                "/home/jenkins/.m2/:/var/jenkins_home/.m2/:rw",
                "-v",
                "/home/jenkins/.ssh/:/var/jenkins_home/.ssh/:ro",
                "-v",
                "/home/jenkins/.gitconfig:/var/jenkins_home/.gitconfig:ro",
                "-v",
                "/home/jenkins/.netrc:/var/jenkins_home/.netrc:ro",
                "-d",
                "localhost/automatons",
                "/var/jenkins_home/workspace/eap-7.4.x-testsuite/hera/wait.sh"
            ],
            "Umask": "0022",
            "Timeout": 0,
            "StopTimeout": 10
        },
        "HostConfig": {
            "Binds": [
                "/opt:/opt:ro,rprivate,rbind",
                "/home/jenkins/.m2:/var/jenkins_home/.m2/:rw,rprivate,rbind",
                "/home/jenkins/.ssh:/var/jenkins_home/.ssh/:ro,rprivate,rbind",
                "/home/jenkins/.gitconfig:/var/jenkins_home/.gitconfig:ro,rprivate,rbind",
                "/home/jenkins/.netrc:/var/jenkins_home/.netrc:ro,rprivate,rbind",
                "/home/jenkins/current/jobs/eap-7.4.x-build/builds/7/archive:/parent_job/:ro,rprivate,rbind",
                "/home/jenkins/current/workspace/eap-7.4.x-testsuite:/var/jenkins_home/workspace/eap-7.4.x-testsuite:rw,rprivate,rbind"
            ],
            "CgroupManager": "cgroupfs",
            "CgroupMode": "host",
            "ContainerIDFile": "",
            "LogConfig": {
                "Type": "k8s-file",
                "Config": null,
                "Path": "/home/jenkins/.local/share/containers/storage/overlay-containers/1a2b19d8915046a04773d7ac350c95d861bcb295d06e9ea2558178eaaa10a1ac/userdata/ctr.log",
                "Tag": "",
                "Size": "0B"
            },
            "NetworkMode": "slirp4netns",
            "PortBindings": {},
            "RestartPolicy": {
                "Name": "",
                "MaximumRetryCount": 0
            },
            "AutoRemove": true,
            "VolumeDriver": "",
            "VolumesFrom": null,
            "CapAdd": [],
            "CapDrop": [
                "CAP_AUDIT_WRITE",
                "CAP_MKNOD"
            ],
            "Dns": [],
            "DnsOptions": [],
            "DnsSearch": [],
            "ExtraHosts": [
                "olympus:10.88.0.1"
            ],
            "GroupAdd": [],
            "IpcMode": "private",
            "Cgroup": "",
            "Cgroups": "default",
            "Links": null,
            "OomScoreAdj": 0,
            "PidMode": "private",
            "Privileged": false,
            "PublishAllPorts": false,
            "ReadonlyRootfs": false,
            "SecurityOpt": [],
            "Tmpfs": {},
            "UTSMode": "private",
            "UsernsMode": "private",
            "ShmSize": 65536000,
            "Runtime": "oci",
            "ConsoleSize": [
                0,
                0
            ],
            "Isolation": "",
            "CpuShares": 0,
            "Memory": 0,
            "NanoCpus": 0,
            "CgroupParent": "",
            "BlkioWeight": 0,
            "BlkioWeightDevice": null,
            "BlkioDeviceReadBps": null,
            "BlkioDeviceWriteBps": null,
            "BlkioDeviceReadIOps": null,
            "BlkioDeviceWriteIOps": null,
            "CpuPeriod": 0,
            "CpuQuota": 0,
            "CpuRealtimePeriod": 0,
            "CpuRealtimeRuntime": 0,
            "CpusetCpus": "",
            "CpusetMems": "",
            "Devices": [],
            "DiskQuota": 0,
            "KernelMemory": 0,
            "MemoryReservation": 0,
            "MemorySwap": 0,
            "MemorySwappiness": 0,
            "OomKillDisable": false,
            "PidsLimit": 0,
            "Ulimits": [],
            "CpuCount": 0,
            "CpuPercent": 0,
            "IOMaximumIOps": 0,
            "IOMaximumBandwidth": 0,
            "CgroupConf": null
        }
    }
]

proc_cgroups

#subsys_name	hierarchy	num_cgroups	enabled
cpuset	6	4	1
cpu	8	126	1
cpuacct	8	126	1
blkio	11	126	1
memory	9	167	1
devices	3	126	1
freezer	7	4	1
net_cls	5	4	1
perf_event	4	4	1
net_prio	5	4	1
hugetlb	2	4	1
pids	10	159	1
rdma	12	1	1

proc_self_cgroup

12:rdma:/
11:blkio:/system.slice/sshd.service
10:pids:/user.slice/user-1000.slice/session-3.scope
9:memory:/user.slice/user-1000.slice/session-3.scope
8:cpu,cpuacct:/
7:freezer:/
6:cpuset:/
5:net_cls,net_prio:/
4:perf_event:/
3:devices:/system.slice/sshd.service
2:hugetlb:/
1:name=systemd:/user.slice/user-1000.slice/[email protected]/user.slice/podman-637674.scope

proc_self_mountinfo

931 921 0:86 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,context="system_u:object_r:container_file_t:s0:c375,c611",mode=755,uid=100000,gid=100000
932 931 0:26 /user.slice/user-1000.slice/[email protected]/user.slice/podman-637196.scope/2be1ee6e076d20b38a61a1e3289974662d646fb50489ccf22f7fa4e3dc082295 /sys/fs/cgroup/systemd ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd
933 931 0:29 / /sys/fs/cgroup/hugetlb ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,hugetlb
934 931 0:30 /user.slice /sys/fs/cgroup/devices ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,devices
935 931 0:31 / /sys/fs/cgroup/perf_event ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,perf_event
936 931 0:32 / /sys/fs/cgroup/net_cls,net_prio ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,net_cls,net_prio
937 931 0:33 / /sys/fs/cgroup/cpuset ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,cpuset
938 931 0:34 / /sys/fs/cgroup/freezer ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,freezer
940 931 0:35 /user.slice /sys/fs/cgroup/cpu,cpuacct ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,cpu,cpuacct
941 931 0:36 /user.slice/user-1000.slice/session-50.scope /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,memory
942 931 0:37 /user.slice/user-1000.slice/session-50.scope /sys/fs/cgroup/pids ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,pids
943 931 0:38 /user.slice /sys/fs/cgroup/blkio ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,blkio
944 931 0:39 / /sys/fs/cgroup/rdma ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,rdma

Z_cgroup_v1_npe_when_cgrouppath_does_not_start_with_mount_root.patch

diff --git a/test/jdk/jdk/internal/platform/cgroup/TestCgroupSubsystemFactory.java b/test/jdk/jdk/internal/platform/cgroup/TestCgroupSubsystemFactory.java
index 369d4244533..a84cb70d7f5 100644
--- a/test/jdk/jdk/internal/platform/cgroup/TestCgroupSubsystemFactory.java
+++ b/test/jdk/jdk/internal/platform/cgroup/TestCgroupSubsystemFactory.java
@@ -43,6 +43,7 @@ import jdk.internal.platform.CgroupSubsystemFactory;
 import jdk.internal.platform.CgroupSubsystemFactory.CgroupTypeResult;
 import jdk.internal.platform.CgroupV1MetricsImpl;
 import jdk.internal.platform.cgroupv1.CgroupV1Subsystem;
+import jdk.internal.platform.cgroupv1.CgroupV1SubsystemController;
 import jdk.internal.platform.Metrics;
 import jdk.test.lib.Utils;
 import jdk.test.lib.util.FileUtils;
@@ -72,8 +73,10 @@ public class TestCgroupSubsystemFactory {
     private Path cgroupv1MntInfoDoubleCpusets;
     private Path cgroupv1MntInfoDoubleCpusets2;
     private Path cgroupv1MntInfoColonsHierarchy;
+    private Path cgroupv1MntInfoPrefix;
     private Path cgroupv1SelfCgroup;
     private Path cgroupv1SelfColons;
+    private Path cgroupv1SelfPrefix;
     private Path cgroupv2SelfCgroup;
     private Path cgroupv1SelfCgroupJoinCtrl;
     private Path cgroupv1CgroupsOnlyCPUCtrl;
@@ -166,6 +169,20 @@ public class TestCgroupSubsystemFactory {
             "42 30 0:38 / /sys/fs/cgroup/cpuset rw,nosuid,nodev,noexec,relatime shared:14 - cgroup none rw,seclabel,cpuset\n" +
             "43 30 0:39 / /sys/fs/cgroup/blkio rw,nosuid,nodev,noexec,relatime shared:15 - cgroup none rw,seclabel,blkio\n" +
             "44 30 0:40 / /sys/fs/cgroup/freezer rw,nosuid,nodev,noexec,relatime shared:16 - cgroup none rw,seclabel,freezer\n";
+    private String mntInfoPrefix =
+            "931 921 0:86 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime - tmpfs tmpfs rw,context=\"system_u:object_r:container_file_t:s0:c375,c611\",mode=755,uid=100000,gid=100000\n" +
+            "932 931 0:26 /user.slice/user-1000.slice/[email protected]/user.slice/podman-637196.scope/2be1ee6e076d20b38a61a1e3289974662d646fb50489ccf22f7fa4e3dc082295 /sys/fs/cgroup/systemd ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd\n" +
+            "933 931 0:29 / /sys/fs/cgroup/hugetlb ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,hugetlb\n" +
+            "934 931 0:30 /user.slice /sys/fs/cgroup/devices ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,devices\n" +
+            "935 931 0:31 / /sys/fs/cgroup/perf_event ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,perf_event\n" +
+            "936 931 0:32 / /sys/fs/cgroup/net_cls,net_prio ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,net_cls,net_prio\n" +
+            "937 931 0:33 / /sys/fs/cgroup/cpuset ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,cpuset\n" +
+            "938 931 0:34 / /sys/fs/cgroup/freezer ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,freezer\n" +
+            "940 931 0:35 /user.slice /sys/fs/cgroup/cpu,cpuacct ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,cpu,cpuacct\n" +
+            "941 931 0:36 /user.slice/user-1000.slice/session-50.scope /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,memory\n" +
+            "942 931 0:37 /user.slice/user-1000.slice/session-50.scope /sys/fs/cgroup/pids ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,pids\n" +
+            "943 931 0:38 /user.slice /sys/fs/cgroup/blkio ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,blkio\n" +
+            "944 931 0:39 / /sys/fs/cgroup/rdma ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,rdma";
     private String cgroupsNonZeroHierarchy =
             "#subsys_name hierarchy   num_cgroups enabled\n" +
             "cpuset  9   1   1\n" +
@@ -217,6 +234,19 @@ public class TestCgroupSubsystemFactory {
             "2:cpu,cpuacct:/\n" +
             "1:name=systemd:/user.slice/user-1000.slice/[email protected]/apps.slice/apps-org.gnome.Terminal.slice/vte-spawn-3c00b338-5b65-439f-8e97-135e183d135d.scope\n" +
             "0::/user.slice/user-1000.slice/[email protected]/apps.slice/apps-org.gnome.Terminal.slice/vte-spawn-3c00b338-5b65-439f-8e97-135e183d135d.scope\n";
+    private  String cgroupv1SelfPrefixContent =
+            "12:rdma:/\n" +
+            "11:blkio:/system.slice/sshd.service\n" +
+            "10:pids:/user.slice/user-1000.slice/session-3.scope\n" +
+            "9:memory:/user.slice/user-1000.slice/session-3.scope\n" +
+            "8:cpu,cpuacct:/\n" +
+            "7:freezer:/\n" +
+            "6:cpuset:/\n" +
+            "5:net_cls,net_prio:/\n" +
+            "4:perf_event:/\n" +
+            "3:devices:/system.slice/sshd.service\n" +
+            "2:hugetlb:/\n" +
+            "1:name=systemd:/user.slice/user-1000.slice/[email protected]/user.slice/podman-637674.scope";
     private String cgroupv2SelfCgroupContent = "0::/user.slice/user-1000.slice/session-2.scope";
 
     @Before
@@ -257,12 +287,18 @@ public class TestCgroupSubsystemFactory {
             cgroupv1MntInfoColonsHierarchy = Paths.get(existingDirectory.toString(), "mountinfo_colons");
             Files.writeString(cgroupv1MntInfoColonsHierarchy, mntInfoColons);
 
+            cgroupv1MntInfoPrefix = Paths.get(existingDirectory.toString(), "mountinfo-prefix");
+            Files.writeString(cgroupv1MntInfoPrefix, mntInfoPrefix);
+
             cgroupv1SelfCgroup = Paths.get(existingDirectory.toString(), "self_cgroup_cgv1");
             Files.writeString(cgroupv1SelfCgroup, cgroupv1SelfCgroupContent);
 
             cgroupv1SelfColons = Paths.get(existingDirectory.toString(), "self_colons_cgv1");
             Files.writeString(cgroupv1SelfColons, cgroupv1SelfColonsContent);
 
+            cgroupv1SelfPrefix = Paths.get(existingDirectory.toString(), "self_prefix_cgv1");
+            Files.writeString(cgroupv1SelfPrefix, cgroupv1SelfPrefixContent);
+
             cgroupv2SelfCgroup = Paths.get(existingDirectory.toString(), "self_cgroup_cgv2");
             Files.writeString(cgroupv2SelfCgroup, cgroupv2SelfCgroupContent);
 
@@ -393,6 +429,24 @@ public class TestCgroupSubsystemFactory {
         assertEquals(memoryInfo.getMountRoot(), memoryInfo.getCgroupPath());
     }
 
+    @Test
+    public void testMountPrefixCgroupsV1() throws IOException {
+        String cgroups = cgroupv1CgInfoNonZeroHierarchy.toString();
+        String mountInfo = cgroupv1MntInfoPrefix.toString();
+        String selfCgroup = cgroupv1SelfPrefix.toString();
+        Optional<CgroupTypeResult> result = CgroupSubsystemFactory.determineType(mountInfo, cgroups, selfCgroup);
+
+        assertTrue("Expected non-empty cgroup result", result.isPresent());
+        CgroupTypeResult res = result.get();
+        CgroupInfo memoryInfo = res.getInfos().get("memory");
+        assertEquals(memoryInfo.getCgroupPath(), "/user.slice/user-1000.slice/session-3.scope");
+        assertEquals("/sys/fs/cgroup/memory", memoryInfo.getMountPoint());
+        CgroupV1SubsystemController cgroupv1MemoryController = new CgroupV1SubsystemController(memoryInfo.getMountRoot(), memoryInfo.getMountPoint());
+        cgroupv1MemoryController.setPath(memoryInfo.getCgroupPath());
+        // issue to verify: path was not set because the cgroupPath does not start with mount root
+        assertNotNull(cgroupv1MemoryController.path());
+    }
+
     @Test
     public void testZeroHierarchyCgroupsV1() throws IOException {
         String cgroups = cgroupv1CgInfoZeroHierarchy.toString();

Thanks, @jerboaa here is the report running in the affected container:

[jenkins@383e373c4282 jenkins_home]$ cat /proc/self/cgroup |grep memory
11:memory:/user.slice/user-1000.slice/session-3.scope
[jenkins@383e373c4282 jenkins_home]$ cat /proc/self/mountinfo |grep memory
916 905 0:38 /user.slice/user-1000.slice/session-31.scope /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,seclabel,memory

[jenkins@383e373c4282 jenkins_home]$ /opt/oracle/jdk-17.0.2/bin/java -version
openjdk version "17.0.2" 2022-01-18
OpenJDK Runtime Environment (build 17.0.2+8-86)
OpenJDK 64-Bit Server VM (build 17.0.2+8-86, mixed mode, sharing)

[jenkins@383e373c4282 jenkins_home]$ /opt/oracle/jdk-17.0.2/bin/java FindCgroupPath.java /sys/fs/cgroup/memory
PID is: 452 walking: /sys/fs/cgroup/memory
Analyzing /sys/fs/cgroup/memory/cgroup.procs

[jenkins@383e373c4282 jenkins_home]$ cat /sys/fs/cgroup/memory/cgroup.procs
1
609

@gaol Thank you. This output:

[jenkins@383e373c4282 jenkins_home]$ /opt/oracle/jdk-17.0.2/bin/java FindCgroupPath.java /sys/fs/cgroup/memory
PID is: 452 walking: /sys/fs/cgroup/memory
Analyzing /sys/fs/cgroup/memory/cgroup.procs

Suggests that the current process isn't being part of the memory namespace. If it was, the output would be something like this:

bash-5.1$ /opt/jdk/bin/java FindCgroupPath.java /sys/fs/cgroup/memory
PID is: 2 walking: /sys/fs/cgroup/memory
Analyzing /sys/fs/cgroup/memory/cgroup.procs
Found process at path /sys/fs/cgroup/memory/cgroup.procs
Cgroup path is: /sys/fs/cgroup/memory

May I know if this is the wrong set up in your opinion ? where to check the memory limitation of the process inside of the container in current setup ? thanks !

No, it should be fine. I'm guessing that some other controllers would be enabled. Either way, OpenJDK needs to handle this case properly. The question is which (if any of the relevant ones) is indeed enabled. You could find out with something like this:

for c in $(ls -d /sys/fs/cgroup/*); do if echo $c | grep -qE 'memory|cpu|blkio|pids'; then java FindCgroupPath.java $c; fi; done

@gaol, since you are running on a cgroupv1 system, I think this problem can be worked around by running with podman ... --cgroupns=private ...

See https://docs.podman.io/en/latest/markdown/podman-run.1.html

--cgroupns=mode: Set the cgroup namespace mode for the container.
    host: use the host’s cgroup namespace inside the container.
    container:id: join the namespace of the specified container.
    private: create a new cgroup namespace.
    ns:path: join the namespace at the specified path.
If the host uses cgroups v1, the default is set to host. On cgroups v2, the default is private.

By default, if you don't use any memory settings, on a cgroupv1 system, podman puts the containerized process into the memory cgroup of the user on the host. Here's what I get:

U2110: ~$ cat /proc/self/cgroup | grep memory
7:memory:/user.slice/user-1000.slice/session-3.scope
U2110: ~$ cat /proc/self/mountinfo | grep memory
43 32 0:38 / /sys/fs/cgroup/memory rw,nosuid,nodev,noexec,relatime shared:21 - cgroup cgroup rw,memory

U2110: ~$ podman run --rm -it --tty=true fedora bash
[root@dc24d11dcb5e /]# cat /proc/self/cgroup | grep memory
7:memory:/user.slice/user-1000.slice/[email protected]
[root@dc24d11dcb5e /]# cat /proc/self/mountinfo | grep memory
1181 1174 0:38 /user.slice/user-1000.slice/[email protected] /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,memory

Note that I used ssh to log onto the host U2110 and /user.slice/user-1000.slice/session-3.scope is the cgroup hierarchy used for this SSH session.

I think in you case, you use one SSH session to create the container, but use another SSH session to launch the Java process. For some unknown reason, podman uses the hierarchy of the SSH session (instead of /user.slice/user-1000.slice/[email protected] in my case). This causes the JVM to fail.

If you use --cgroupns=private, the cgroup and mountinfo should look like this and will make Java happy.

U2110: ~$ podman run --rm -it --tty=true --cgroupns=private fedora bash
[root@d14b44b4d754 /]# cat /proc/self/cgroup | grep memory
7:memory:/
[root@d14b44b4d754 /]# cat /proc/self/mountinfo | grep memory
1181 1174 0:38 / /sys/fs/cgroup/memory ro,nosuid,nodev,noexec,relatime - cgroup cgroup rw,memory

@jerboaa I think we should reconsider how we process the mountpoint in mountinfo. If it's not '/', and the path doesn't exist (not in the filesystem namespace of the current process), I don't think we should interpret it at all.

I think in you case, you use one SSH session to create the container, but use another SSH session to launch the Java process

Thanks @iklam
Yes, this is exactly what we do. 👍

Currently we use -v /sys/fs/cgroup:/sys/fs/cgroup:ro to bypass the failure, I will do experiment on the --cgroupns=private.

for c in $(ls -d /sys/fs/cgroup/*); do if echo $c | grep -qE 'memory|cpu|blkio|pids'; then java FindCgroupPath.java $c; fi; done

@jerboaa below are the report using the script above:

[jenkins@8b078952dce0 jenkins_home]$ for c in $(ls -d /sys/fs/cgroup/*); do if echo $c | grep -qE 'memory|cpu|blkio|pids'; then /opt/oracle/jdk-17.0.2/bin/java FindCgroupPath.java $c; fi; done
PID is: 248 walking: /sys/fs/cgroup/blkio
Analyzing /sys/fs/cgroup/blkio/cgroup.procs
Found process at path /sys/fs/cgroup/blkio/cgroup.procs
Cgroup path is: /sys/fs/cgroup/blkio
PID is: 272 walking: /sys/fs/cgroup/cpu
PID is: 296 walking: /sys/fs/cgroup/cpu,cpuacct
Analyzing /sys/fs/cgroup/cpu,cpuacct/cgroup.procs
Found process at path /sys/fs/cgroup/cpu,cpuacct/cgroup.procs
Cgroup path is: /sys/fs/cgroup/cpu,cpuacct
PID is: 320 walking: /sys/fs/cgroup/cpuacct
PID is: 344 walking: /sys/fs/cgroup/cpuset
Analyzing /sys/fs/cgroup/cpuset/cgroup.procs
Found process at path /sys/fs/cgroup/cpuset/cgroup.procs
Cgroup path is: /sys/fs/cgroup/cpuset
PID is: 375 walking: /sys/fs/cgroup/memory
Analyzing /sys/fs/cgroup/memory/cgroup.procs
PID is: 407 walking: /sys/fs/cgroup/pids
Analyzing /sys/fs/cgroup/pids/cgroup.procs
[jenkins@8b078952dce0 jenkins_home]$ /opt/oracle/jdk-17.0.2/bin/java -XshowSettings:system -version
Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/sun.nio.fs.UnixFileSystem.getPath(UnixFileSystem.java:263)
	at java.base/java.nio.file.Path.of(Path.java:147)
	at java.base/java.nio.file.Paths.get(Paths.java:69)
	at java.base/jdk.internal.platform.CgroupUtil.lambda$readStringValue$1(CgroupUtil.java:67)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:569)
	at java.base/jdk.internal.platform.CgroupUtil.readStringValue(CgroupUtil.java:69)
	at java.base/jdk.internal.platform.CgroupSubsystemController.getStringValue(CgroupSubsystemController.java:65)
	at java.base/jdk.internal.platform.CgroupSubsystemController.getLongValue(CgroupSubsystemController.java:124)
	at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getLongValue(CgroupV1Subsystem.java:175)
	at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getHierarchical(CgroupV1Subsystem.java:149)
	at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.initSubSystem(CgroupV1Subsystem.java:84)
	at java.base/jdk.internal.platform.cgroupv1.CgroupV1Subsystem.getInstance(CgroupV1Subsystem.java:60)
	at java.base/jdk.internal.platform.CgroupSubsystemFactory.create(CgroupSubsystemFactory.java:116)
	at java.base/jdk.internal.platform.CgroupMetrics.getInstance(CgroupMetrics.java:167)
	at java.base/jdk.internal.platform.SystemMetrics.instance(SystemMetrics.java:29)
	at java.base/jdk.internal.platform.Metrics.systemMetrics(Metrics.java:58)
	at java.base/jdk.internal.platform.Container.metrics(Container.java:43)
	at java.base/sun.launcher.LauncherHelper.printSystemMetrics(LauncherHelper.java:318)
	at java.base/sun.launcher.LauncherHelper.showSettings(LauncherHelper.java:173)

After using --cgroupns=private, the output becomes:

[jenkins@3cfd6c2aaac0 jenkins_home]$ for c in $(ls -d /sys/fs/cgroup/*); do if echo $c | grep -qE 'memory|cpu|blkio|pids'; then /opt/oracle/jdk-17.0.2/bin/java FindCgroupPath.java $c; fi; done
PID is: 214 walking: /sys/fs/cgroup/blkio
Analyzing /sys/fs/cgroup/blkio/cgroup.procs
Found process at path /sys/fs/cgroup/blkio/cgroup.procs
Cgroup path is: /sys/fs/cgroup/blkio
PID is: 238 walking: /sys/fs/cgroup/cpu
PID is: 262 walking: /sys/fs/cgroup/cpu,cpuacct
Analyzing /sys/fs/cgroup/cpu,cpuacct/cgroup.procs
Found process at path /sys/fs/cgroup/cpu,cpuacct/cgroup.procs
Cgroup path is: /sys/fs/cgroup/cpu,cpuacct
PID is: 286 walking: /sys/fs/cgroup/cpuacct
PID is: 310 walking: /sys/fs/cgroup/cpuset
Analyzing /sys/fs/cgroup/cpuset/cgroup.procs
Found process at path /sys/fs/cgroup/cpuset/cgroup.procs
Cgroup path is: /sys/fs/cgroup/cpuset
PID is: 340 walking: /sys/fs/cgroup/memory
Analyzing /sys/fs/cgroup/memory/cgroup.procs
PID is: 372 walking: /sys/fs/cgroup/pids
Analyzing /sys/fs/cgroup/pids/cgroup.procs
[jenkins@3cfd6c2aaac0 jenkins_home]$ /opt/oracle/jdk-17.0.2/bin/java -XshowSettings:system -version
Operating System Metrics:
    Provider: cgroupv1
    Effective CPU Count: 2
    CPU Period: 100000us
    CPU Quota: -1
    CPU Shares: -1
    List of Processors, 2 total: 
    0 1 
    List of Effective Processors, 2 total: 
    0 1 
    List of Memory Nodes, 1 total: 
    0 
    List of Available Memory Nodes, 1 total: 
    0 
    Memory Limit: Unlimited
    Memory Soft Limit: Unlimited
    Memory & Swap Limit: Unlimited

openjdk version "17.0.2" 2022-01-18
OpenJDK Runtime Environment (build 17.0.2+8-86)
OpenJDK 64-Bit Server VM (build 17.0.2+8-86, mixed mode, sharing)

@jerboaa I think we should reconsider how we process the mountpoint in mountinfo. If it's not '/', and the path doesn't exist (not in the filesystem namespace of the current process), I don't think we should interpret it at all.

@iklam Let's discuss this in https://bugs.openjdk.java.net/browse/JDK-8286212. I have no idea how transient gists are. It's not clear what you mean. Do you mean the root field or the mount point field according to man procfs (i.e. field (4) or (5)? Because we always need to consider (5) on cgroups v1 IMO.

@jerboaa I think we should reconsider how we process the mountpoint in mountinfo. If it's not '/', and the path doesn't exist (not in the filesystem namespace of the current process), I don't think we should interpret it at all.

@iklam Let's discuss this in https://bugs.openjdk.java.net/browse/JDK-8286212. I have no idea how transient gists are. It's not clear what you mean. Do you mean the root field or the mount point field according to man procfs (i.e. field (4) or (5)? Because we always need to consider (5) on cgroups v1 IMO.

Yes, I meant the root field (4).

OK. I'll consider this when rebooting the PR.