前言

今天遇到一个问题，应用工程师分析是系统层的问题，然后就把这个锅给了我。最后我又把锅甩回给了应用工程师。

异常log如下:

I [2019-08-18 10:11:08 GMT+8] binder: 1433:1561 transaction failed 29201/-28, size 828-8 line 3135
W BroadcastQueue: Can't deliver broadcast to com.xxxx.xxxxx (pid 4712). Crashing it.
W BroadcastQueue: Failure sending broadcast Intent { act=android.intent.action.BATTERY_CHANGED flg=0x60000010 (has extras) }
W BroadcastQueue: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died
W BroadcastQueue:   at android.os.BinderProxy.transactNative(Native Method)
W BroadcastQueue:   at android.os.BinderProxy.transact(Binder.java:1127)
W BroadcastQueue:   at android.app.IApplicationThread$Stub$Proxy.scheduleRegisteredReceiver(IApplicationThread.java:1237)
W BroadcastQueue:   at com.android.server.am.BroadcastQueue.performReceiveLocked(BroadcastQueue.java:496)
W BroadcastQueue:   at com.android.server.am.BroadcastQueue.deliverToRegisteredReceiverLocked(BroadcastQueue.java:715)
W BroadcastQueue:   at com.android.server.am.BroadcastQueue.processNextBroadcastLocked(BroadcastQueue.java:875)
W BroadcastQueue:   at com.android.server.am.BroadcastQueue.processNextBroadcast(BroadcastQueue.java:834)
W BroadcastQueue:   at com.android.server.am.BroadcastQueue$BroadcastHandler.handleMessage(BroadcastQueue.java:172)
W BroadcastQueue:   at android.os.Handler.dispatchMessage(Handler.java:106)
W BroadcastQueue:   at android.os.Looper.loop(Looper.java:193)
W BroadcastQueue:   at android.os.HandlerThread.run(HandlerThread.java:65)
W BroadcastQueue:   at com.android.server.ServiceThread.run(ServiceThread.java:44)

初步分析

从log来看的确好像是binder驱动第3135行出现问题（line 3135）

binder: 1433:1561 transaction failed 29201/-28, size 828-8 line 3135

一看Binder.c的代码发现对不上3135行，估计是编译版本不一样，因为测试是user版本，代码优化了，这怎么办？我需要在userdebug的版本上你复现此问题。

Binder.c
3129    if (target_node && target_node->txn_security_ctx) {
3130              u32 secid;
3131           size_t added_size;
3133            security_task_getsecid(proc->tsk, &secid);
3134         ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
3135           if (ret) {
3136                  return_error = BR_FAILED_REPLY;
3137                    return_error_param = ret;
3138                    return_error_line = __LINE__;
3139                        goto err_get_secctx_failed;
3140            }

聪明机智的我瞬间判断应该是对应到3164行，应该是binder server无法申请足够的buffer，别问我怎么想到的，有时候解决问题就得靠猜。

3154    t->buffer = binder_alloc_new_buf(&target_proc->alloc, tr->data_size,
3155           tr->offsets_size, extra_buffers_size,
3156             !reply && (t->flags & TF_ONE_WAY));
3157       if (IS_ERR(t->buffer)) {
3158                /*
3159            * -ESRCH indicates VMA cleared. The target is dying.
3160              */
3161         return_error_param = PTR_ERR(t->buffer);
3162          return_error = return_error_param == -ESRCH ?
3163                    BR_DEAD_REPLY : BR_FAILED_REPLY;
3164             return_error_line = __LINE__;
3165         t->buffer = NULL;
3166         goto err_binder_alloc_buf_failed;
3167       }

为了证明我判断是对的，我写了如下的一个demo安装到userdebug来制造binder server无法申请足够的buffer的情况

public class MainActivity extends Activity implements View.OnClickListener {
    private MyLinear mRoot;
    private IMyAidlInterface myAidlInterface;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRoot = (MyLinear) findViewById(R.id.root);
        mRoot.setOnClickListener(this);
        Intent intent = new Intent(this, MyService.class);
        bindService(intent, new ServiceConnection() {
            @Override
            public void onServiceConnected(ComponentName name, IBinder service) {
                myAidlInterface = IMyAidlInterface.Stub.asInterface(service);
            @Override
            public void onServiceDisconnected(ComponentName name) {
        }, Context.BIND_AUTO_CREATE);
    @Override
    public void onClick(View v) {
        try {
            while (true) {
                myAidlInterface.send("dfdafsdfafdasdfadfadsfafd");
        } catch (Exception e) {
public class MyService extends Service {
    @Override
    public IBinder onBind(Intent intent) {
        return new MyBinder();
    public class MyBinder extends IMyAidlInterface.Stub {
        @Override
        public void send(String e) throws RemoteException {
            //后面发现这个4秒的卡顿，不加也可以复现此问题
            try {
                Thread.sleep(4000);
            } catch (Exception ee) {
// IMyAidlInterface.aidl
package com.tct.activitydemo;
// Declare any non-default types here with import statements
interface IMyAidlInterface {
     * Demonstrates some basic types that you can use as parameters
     * and return values in AIDL.
    oneway void send(String e);
}

出现的异常log，和之前log相比，除了行数不对，error code是一样的都是29201/-28，而且行数果然是3164行，所以我的推测是对的。

//binder: 1433:1561 transaction failed 29201/-28, size 828-8 line 3135
binder: 30286:30286 transaction failed 29201/-28, size 140-0 line 3164

初步分析结论

广播的发送失败是原因，在一次binder通信中，无法向广播注册的App的binder驱动中映射的共享内存申请足够buffer。

重大发现

我发现出问题的应用注册了300多个广播，都是监听android.intent.action.BATTERY_CHANGED，具体log就不贴了，在bugreport中会有当前系统所有广播的dumpsys的信息。我贴出meminfo的信息，发现三百多个activity没有被GC，因为那个广播是在activity中被动态注册的，所以变相可以证明注册了300多个广播

** MEMINFO in pid 4712 [com.xxxxxxxxxxx] **
.....省略没用的信息，看下面activity的数量是325 
 Objects
               Views:    13600         ViewRootImpl:        2
         AppContexts:      329           Activities:      325
              Assets:        3        AssetManagers:        0
       Local Binders:      352        Proxy Binders:      366
       Parcel memory:      887         Parcel count:     2235
    Death Recipients:        2      OpenSSL Sockets:        0
            WebViews:        0

推测

当这个广播发送的时候，由于他的接受者有300多个，每一次接收都会在申请一次buffer，如果短时间一下子申请，非常有可能超过binder驱动的(1mb-8kb)/2的限制，有人会问为什么是(1mb-8kb)/2而不是1mb-8kb，因为scheduleRegisteredReceiver是oneway的，对这个有疑问的，可以看一下我的另外一个文章： [007]一次Binder通信最大可以传输多大的数据？

进一步分析

其实一般分析到这里，对于我来说已经可以把锅甩回给了应用层，但是这个问题的好奇心促使我继续分析下去，一定要找到广播重复注册的原因。

涉及的保密，我把应用层代码的精简成自己的代码

public class MyActivity extends Activity {
    private MyReceiver receiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("fdafdafsdafaffasdfad");
        receiver = new MyReceiver(this);
        getApplication().registerReceiver(receiver, intentFilter);
    @Override
    protected void onDestroy() {
        try {
            //因为上下文不同，会导致unregisterReceiver失败，从而导致MyActivity和MyReceiver，无法被GC
            unregisterReceiver(receiver);
        } catch (Exception e) {
        super.onDestroy();
    public static class MyReceiver extends BroadcastReceiver {
        private Context mContext;
        public MyReceiver(Context context) {
            mContext = context;
        @Override