ActivityManager: don't freeze processes holding file locks

As a temporary measure waiting for the more robust b/176927978 to be
implemented, query the file lock status of processes prior freezing
them, and skip freeze if any locks are held.

Test: verified form the logs that processes holding file locks are not
frozen
Bug: 176928302

Change-Id: Ib7e1715effb63c1b304ce22a9451294fd9f7b10d

1 files changed, 37 insertions, 0 deletions

diff --git a/core/java/android/os/Process.java b/core/java/android/os/Process.java
index 8048b9df6097..39e3e146f45b 100644
--- a/core/java/android/os/Process.java
+++ b/core/java/android/os/Process.java
@@ -31,9 +31,12 @@ import dalvik.system.VMRuntime;
 
 import libcore.io.IoUtils;
 
+import java.io.BufferedReader;
 import java.io.FileDescriptor;
+import java.io.FileReader;
 import java.io.IOException;
 import java.util.Map;
+import java.util.StringTokenizer;
 import java.util.concurrent.TimeoutException;
 
 /**
@@ -1430,4 +1433,38 @@ public class Process {
     }
 
     private static native int nativePidFdOpen(int pid, int flags) throws ErrnoException;
+
+    /**
+     * Checks if a process corresponding to a specific pid owns any file locks.
+     * @param pid The process ID for which we want to know the existence of file locks.
+     * @return true If the process holds any file locks, false otherwise.
+     * @throws IOException if /proc/locks can't be accessed.
+     *
+     * @hide
+     */
+    public static boolean hasFileLocks(int pid) throws IOException {
+        BufferedReader br = null;
+
+        try {
+            br = new BufferedReader(new FileReader("/proc/locks"));
+            String line;
+
+            while ((line = br.readLine()) != null) {
+                StringTokenizer st = new StringTokenizer(line);
+
+                for (int i = 0; i < 5 && st.hasMoreTokens(); i++) {
+                    String str = st.nextToken();
+                    if (i == 4 && Integer.parseInt(str) == pid) {
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        } finally {
+            if (br != null) {
+                br.close();
+            }
+        }
+    }
 }