From e38797be847429ef2d60ec0f060d1b4ada0e1a25 Mon Sep 17 00:00:00 2001
From: Florian Mayer <fmayer@google.com>
Date: Tue, 11 Feb 2020 17:05:58 +0000
Subject: [PATCH] Do not disable tracing in zygote.

We now use the sequence number of the atrace tag rather than a Binder
transaction, so zygote can observe changes to the tags.

Test: m; flash; adb shell atrace dalvik | grep hprof
Bug: 137366208
Bug: 147667830

Change-Id: I50e32a19c538dd255097c035836504b4746b172b
---
 core/java/android/os/Trace.java                   |  6 +-----
 core/java/com/android/internal/os/Zygote.java     | 10 ----------
 core/java/com/android/internal/os/ZygoteInit.java |  4 ----
 3 files changed, 1 insertion(+), 19 deletions(-)

diff --git a/core/java/android/os/Trace.java b/core/java/android/os/Trace.java
index 25584f1560844..c5c26b0d6482f 100644
--- a/core/java/android/os/Trace.java
+++ b/core/java/android/os/Trace.java
@@ -175,11 +175,7 @@ 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.
-     *
+     * Set whether tracing is enabled in this process.
      * @hide
      */
     public static void setTracingEnabled(boolean enabled, int debugFlags) {
diff --git a/core/java/com/android/internal/os/Zygote.java b/core/java/com/android/internal/os/Zygote.java
index e298556617df7..dfd700f511037 100644
--- a/core/java/com/android/internal/os/Zygote.java
+++ b/core/java/com/android/internal/os/Zygote.java
@@ -279,10 +279,8 @@ public final class Zygote {
                 uid, gid, gids, runtimeFlags, rlimits, mountExternal, seInfo, niceName, fdsToClose,
                 fdsToIgnore, startChildZygote, instructionSet, appDataDir, isTopApp,
                 pkgDataInfoList);
-        // Enable tracing as soon as possible for the child process.
         if (pid == 0) {
             Zygote.disableExecuteOnly(targetSdkVersion);
-            Trace.setTracingEnabled(true, runtimeFlags);
 
             // Note that this event ends at the end of handleChildProc,
             Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "PostFork");
@@ -334,9 +332,6 @@ public final class Zygote {
                 niceName, startChildZygote, instructionSet, appDataDir, isTopApp,
                 pkgDataInfoList);
 
-        // Enable tracing as soon as possible for the child process.
-        Trace.setTracingEnabled(true, runtimeFlags);
-
         // Note that this event ends at the end of handleChildProc.
         Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "PostFork");
 
@@ -393,11 +388,6 @@ public final class Zygote {
                 uid, gid, gids, runtimeFlags, rlimits,
                 permittedCapabilities, effectiveCapabilities);
 
-        // Enable tracing as soon as we enter the system_server.
-        if (pid == 0) {
-            Trace.setTracingEnabled(true, runtimeFlags);
-        }
-
         // Set the Java Language thread priority to the default value for new apps.
         Thread.currentThread().setPriority(Thread.NORM_PRIORITY);
 
diff --git a/core/java/com/android/internal/os/ZygoteInit.java b/core/java/com/android/internal/os/ZygoteInit.java
index 7b6262b5e0d81..ae54eb210de72 100644
--- a/core/java/com/android/internal/os/ZygoteInit.java
+++ b/core/java/com/android/internal/os/ZygoteInit.java
@@ -914,10 +914,6 @@ public class ZygoteInit {
             bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC
 
             bootTimingsTraceLog.traceEnd(); // ZygoteInit
-            // Disable tracing so that forked processes do not inherit stale tracing tags from
-            // Zygote.
-            Trace.setTracingEnabled(false, 0);
-
 
             Zygote.initNativeState(isPrimaryZygote);