YARN-6433. Only accessible cgroup mount directories should be selected for a controller. (Miklos Szegedi via kasha)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/linux/resources/CGroupsHandlerImpl.java

@@ -236,7 +236,12 @@ class CGroupsHandlerImpl implements CGroupsHandler {
       Map<String, List<String>> entries) {
     for (Map.Entry<String, List<String>> e : entries.entrySet()) {
       if (e.getValue().contains(controller)) {
-        return e.getKey();
+        if (new File(e.getKey()).canRead()) {
+          return e.getKey();
+        } else {
+          LOG.warn(String.format(
+              "Skipping inaccessible cgroup mount point %s", e.getKey()));
+        }
       }
     }
 

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/test/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/linux/resources/TestCGroupsHandlerImpl.java

@@ -252,6 +252,10 @@ public class TestCGroupsHandlerImpl {
     String cpuMtabContent =
         "none " + parentDir.getAbsolutePath()
             + "/cpu cgroup rw,relatime,cpu 0 0\n";
+    // Mark an empty directory called 'cp' cgroup. It is processed before 'cpu'
+    String cpuMtabContentMissing =
+        "none " + parentDir.getAbsolutePath()
+            + "/cp cgroup rw,relatime,cpu 0 0\n";
     String blkioMtabContent =
         "none " + parentDir.getAbsolutePath()
             + "/blkio cgroup rw,relatime,blkio 0 0\n";
@@ -264,6 +268,7 @@ public class TestCGroupsHandlerImpl {
       }
     }
     FileWriter mtabWriter = new FileWriter(mockMtab.getAbsoluteFile());
+    mtabWriter.write(cpuMtabContentMissing);
     mtabWriter.write(cpuMtabContent);
     mtabWriter.write(blkioMtabContent);
     mtabWriter.close();