--- old/src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java	2020-02-20 20:57:27.811368343 +0100
+++ new/src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java	2020-02-20 20:57:27.667367937 +0100
@@ -32,11 +32,12 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.stream.Stream;
 
 import jdk.internal.platform.cgroupv1.CgroupV1Subsystem;
 import jdk.internal.platform.cgroupv2.CgroupV2Subsystem;
 
-class CgroupSubsystemFactory {
+public class CgroupSubsystemFactory {
 
     private static final String CPU_CTRL = "cpu";
     private static final String CPUACCT_CTRL = "cpuacct";
@@ -45,52 +46,27 @@
     private static final String MEMORY_CTRL = "memory";
 
     static CgroupMetrics create() {
-        Map<String, CgroupInfo> infos = new HashMap<>();
+        CgroupTypeResult result = null;
         try {
-            List<String> lines = CgroupUtil.readAllLinesPrivileged(Paths.get("/proc/cgroups"));
-            for (String line : lines) {
-                if (line.startsWith("#")) {
-                    continue;
-                }
-                CgroupInfo info = CgroupInfo.fromCgroupsLine(line);
-                switch (info.getName()) {
-                case CPU_CTRL:      infos.put(CPU_CTRL, info); break;
-                case CPUACCT_CTRL:  infos.put(CPUACCT_CTRL, info); break;
-                case CPUSET_CTRL:   infos.put(CPUSET_CTRL, info); break;
-                case MEMORY_CTRL:   infos.put(MEMORY_CTRL, info); break;
-                case BLKIO_CTRL:    infos.put(BLKIO_CTRL, info); break;
-                }
-            }
+            result = determineType("/proc/self/mountinfo", "/proc/cgroups");
         } catch (IOException e) {
             return null;
         }
 
-        // For cgroups v1 all controllers need to have non-zero hierarchy id
-        boolean isCgroupsV2 = true;
-        boolean anyControllersEnabled = false;
-        boolean anyCgroupsV2Controller = false;
-        boolean anyCgroupsV1Controller = false;
-        for (CgroupInfo info: infos.values()) {
-            anyCgroupsV1Controller = anyCgroupsV1Controller || info.getHierarchyId() != 0;
-            anyCgroupsV2Controller = anyCgroupsV2Controller || info.getHierarchyId() == 0;
-            isCgroupsV2 = isCgroupsV2 && info.getHierarchyId() == 0;
-            anyControllersEnabled = anyControllersEnabled || info.isEnabled();
-        }
-
         // If no controller is enabled, return no metrics.
-        if (!anyControllersEnabled) {
+        if (!result.isAnyControllersEnabled()) {
             return null;
         }
         // Warn about mixed cgroups v1 and cgroups v2 controllers. The code is
         // not ready to deal with that on a per-controller basis. Return no metrics
         // in that case
-        if (anyCgroupsV1Controller && anyCgroupsV2Controller) {
+        if (result.isAnyCgroupV1Controllers() && result.isAnyCgroupV2Controllers()) {
             Logger logger = System.getLogger("jdk.internal.platform");
             logger.log(Level.DEBUG, "Mixed cgroupv1 and cgroupv2 not supported. Metrics disabled.");
             return null;
         }
 
-        if (isCgroupsV2) {
+        if (result.isCgroupV2()) {
             CgroupSubsystem subsystem = CgroupV2Subsystem.getInstance();
             return subsystem != null ? new CgroupMetrics(subsystem) : null;
         } else {
@@ -98,4 +74,80 @@
             return subsystem != null ? new CgroupV1MetricsImpl(subsystem) : null;
         }
     }
+
+    public static CgroupTypeResult determineType(String mountInfo, String cgroups) throws IOException {
+        Map<String, CgroupInfo> infos = new HashMap<>();
+        List<String> lines = CgroupUtil.readAllLinesPrivileged(Paths.get(cgroups));
+        for (String line : lines) {
+            if (line.startsWith("#")) {
+                continue;
+            }
+            CgroupInfo info = CgroupInfo.fromCgroupsLine(line);
+            switch (info.getName()) {
+            case CPU_CTRL:      infos.put(CPU_CTRL, info); break;
+            case CPUACCT_CTRL:  infos.put(CPUACCT_CTRL, info); break;
+            case CPUSET_CTRL:   infos.put(CPUSET_CTRL, info); break;
+            case MEMORY_CTRL:   infos.put(MEMORY_CTRL, info); break;
+            case BLKIO_CTRL:    infos.put(BLKIO_CTRL, info); break;
+            }
+        }
+        Stream<String> mntInfo = CgroupUtil.readFilePrivileged(Paths.get(mountInfo));
+        boolean anyCgroupMounted = mntInfo.anyMatch(line -> line.contains("cgroup"));
+
+        // For cgroups v2 all controllers need to have zero hierarchy id
+        // and /proc/self/mountinfo needs to have at least one cgroup filesystem
+        // mounted.
+        boolean isCgroupsV2 = true;
+        boolean anyControllersEnabled = false;
+        boolean anyCgroupsV2Controller = false;
+        boolean anyCgroupsV1Controller = false;
+        for (CgroupInfo info: infos.values()) {
+            anyCgroupsV1Controller = anyCgroupsV1Controller || info.getHierarchyId() != 0;
+            anyCgroupsV2Controller = anyCgroupsV2Controller || info.getHierarchyId() == 0;
+            isCgroupsV2 = isCgroupsV2 && info.getHierarchyId() == 0;
+            anyControllersEnabled = anyControllersEnabled || info.isEnabled();
+        }
+
+        // If there are no mounted controllers in mountinfo, but we've only
+        // seen 0 hierarchy IDs in /proc/cgroups, we are on a cgroups v1 system.
+        if (!anyCgroupMounted && isCgroupsV2) {
+            isCgroupsV2 = false;
+            anyCgroupsV1Controller = true;
+            anyCgroupsV2Controller = false;
+        }
+        return new CgroupTypeResult(isCgroupsV2, anyControllersEnabled, anyCgroupsV2Controller, anyCgroupsV1Controller);
+    }
+
+    public static final class CgroupTypeResult {
+        private final boolean isCgroupV2;
+        private final boolean anyControllersEnabled;
+        private final boolean anyCgroupV2Controllers;
+        private final boolean anyCgroupV1Controllers;
+
+        private CgroupTypeResult(boolean isCgroupV2,
+                                 boolean anyControllersEnabled,
+                                 boolean anyCgroupV2Controllers,
+                                 boolean anyCgroupV1Controllers) {
+            this.isCgroupV2 = isCgroupV2;
+            this.anyControllersEnabled = anyControllersEnabled;
+            this.anyCgroupV1Controllers = anyCgroupV1Controllers;
+            this.anyCgroupV2Controllers = anyCgroupV2Controllers;
+        }
+
+        public boolean isCgroupV2() {
+            return isCgroupV2;
+        }
+
+        public boolean isAnyControllersEnabled() {
+            return anyControllersEnabled;
+        }
+
+        public boolean isAnyCgroupV2Controllers() {
+            return anyCgroupV2Controllers;
+        }
+
+        public boolean isAnyCgroupV1Controllers() {
+            return anyCgroupV1Controllers;
+        }
+    }
 }