3 files changed, 30 insertions, 4 deletions
diff --git a/core/java/android/os/Trace.java b/core/java/android/os/Trace.java
index 617f490..3307a8c 100644
--- a/core/java/android/os/Trace.java
+++ b/core/java/android/os/Trace.java
@@ -79,6 +79,7 @@ public final class Trace {
     private static native void nativeAsyncTraceBegin(long tag, String name, int cookie);
     private static native void nativeAsyncTraceEnd(long tag, String name, int cookie);
     private static native void nativeSetAppTracingAllowed(boolean allowed);
+    private static native void nativeSetTracingEnabled(boolean allowed);
 
     static {
         // We configure two separate change callbacks, one in Trace.cpp and one here.  The
@@ -115,10 +116,6 @@ public final class Trace {
      */
     private static long cacheEnabledTags() {
         long tags = nativeGetEnabledTags();
-        if (tags == TRACE_TAG_NOT_READY) {
-            Log.w(TAG, "Unexpected value from nativeGetEnabledTags: " + tags);
-            // keep going
-        }
         sEnabledTags = tags;
         return tags;
     }
@@ -169,6 +166,22 @@ public final class Trace {
     }
 
     /**
+     * Set whether tracing is enabled in this process.  Tracing is disabled shortly after Zygote
+     * initializes and re-enabled after processes fork from Zygote.  This is done because Zygote
+     * has no way to be notified about changes to the tracing tags, and if Zygote ever reads and
+     * caches the tracing tags, forked processes will inherit those stale tags.
+     *
+     * @hide
+     */
+    public static void setTracingEnabled(boolean enabled) {
+        nativeSetTracingEnabled(enabled);
+
+        // Setting whether tracing is enabled may change the tags, so we update the cached tags
+        // here.
+        cacheEnabledTags();
+    }
+
+    /**
      * Writes a trace message to indicate that a given section of code has
      * begun. Must be followed by a call to {@link #traceEnd} using the same
      * tag.
diff --git a/core/java/com/android/internal/os/ZygoteInit.java b/core/java/com/android/internal/os/ZygoteInit.java
index 7eddc9c..2184fd2 100644
--- a/core/java/com/android/internal/os/ZygoteInit.java
+++ b/core/java/com/android/internal/os/ZygoteInit.java
@@ -25,6 +25,7 @@ import android.net.LocalServerSocket;
 import android.os.Debug;
 import android.os.Process;
 import android.os.SystemClock;
+import android.os.Trace;
 import android.util.EventLog;
 import android.util.Log;
 
@@ -528,6 +529,10 @@ public class ZygoteInit {
             // Do an initial gc to clean up after startup
             gc();
 
+            // Disable tracing so that forked processes do not inherit stale tracing tags from
+            // Zygote.
+            Trace.setTracingEnabled(false);
+
             // If requested, start system server directly from Zygote
             if (argv.length != 2) {
                 throw new RuntimeException(argv[0] + USAGE_STRING);
diff --git a/core/jni/android_os_Trace.cpp b/core/jni/android_os_Trace.cpp
index 1315291..01d02c5 100644
--- a/core/jni/android_os_Trace.cpp
+++ b/core/jni/android_os_Trace.cpp
@@ -86,6 +86,11 @@ static void android_os_Trace_nativeSetAppTracingAllowed(JNIEnv* env,
     atrace_set_debuggable(allowed);
 }
 
+static void android_os_Trace_nativeSetTracingEnabled(JNIEnv* env,
+        jclass clazz, jboolean enabled) {
+    atrace_set_tracing_enabled(enabled);
+}
+
 static JNINativeMethod gTraceMethods[] = {
     /* name, signature, funcPtr */
     { "nativeGetEnabledTags",
@@ -109,6 +114,9 @@ static JNINativeMethod gTraceMethods[] = {
     { "nativeSetAppTracingAllowed",
             "(Z)V",
             (void*)android_os_Trace_nativeSetAppTracingAllowed },
+    { "nativeSetTracingEnabled",
+            "(Z)V",
+            (void*)android_os_Trace_nativeSetTracingEnabled },
 };
 
 int register_android_os_Trace(JNIEnv* env) {