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Android插拔U盘导致黑屏问题排查

ds 2025/7/5 10:59:52

问题现象：

车机大屏偶先插拔带音乐的U盘，导致车机系统短暂黑屏的情况。
日志中可以看到vold进程unmount了两次分区，一次是U盘分区，一次是/storage/emulated/0分区：

I vold    : Start killProcesses: /mnt/media_rw/050F-4BB4
I vold    : Start killProcesses: /storage/emulated/0

问题分析：

/storage/emulated/0分区是/sdcard的映射，理论上不应该在系统正常运行期间被unmount掉，查询上面的日志，发现有这样一条：

StorageUserConnection: Service: [ComponentInfo{com.android.providers.media.module/com.android.providers.media.fuse.ExternalStorageServiceImpl}] disconnected. User [0]

看这个日志的意思是StorageManagerService检测到com.android.providers.media.module进程不在了，对应的代码是这样的：

// StorageUserConnection.javapublic void onServiceDisconnected(ComponentName name) {// Service crashed or process was killed, #onServiceConnected will be called// Don't need to re-bind.Slog.i(TAG, "Service: [" + name + "] disconnected. User [" + mUserId + "]");handleDisconnection();}private void handleDisconnection() {// Clear all sessions because we will need a new device fd since// StorageManagerService will reset the device mount state and #startSession// will be called for any required mounts.// Notify StorageManagerService so it can restart all necessary sessionsclose();resetUserSessions();}

跟踪resetUserSessions可以看到这么一条调用栈：

StorageUserConnection::resetUserSessionsStorageManagerService::resetUser
--------------- binder 调用 -------------------
StorageManagerService::resetIfBootedAndConnectedStorageSessionController::onResetIVold::unmount
--------------- binder 调用 -------------------
VolumeBase::unmountEmulatedVolume::doUnmountKillProcessesUsingPathKillProcessesWithOpenFiles

也就是因为com.android.providers.media.module进程被kill了，导致被SystemServer中的StorageManagerService这个BinderService检测到了（通过bindService时传入的mServiceConnection回调到的）

日志再往上找，看下com.android.providers.media.module进程为什么会被kill，看到下面这几条日志：

I vold    : Start KillProcessesUsingPath: public:8,1 /mnt/media_rw/050F-4BB4
I vold    : Start killProcesses: /mnt/media_rw/050F-4BB4
W vold    : Found symlink /proc/2487/fd/93 referencing /mnt/media_rw/050F-4BB4
W vold    : Sending Interrupt to pid 2487 (rs.media.module, /system/bin/app_process64)

可以看到是因为拔掉U盘的时候，触发了Vold的动作，检测到com.android.providers.media.module进程在访问U盘分区中的内容，就把它kill了。

这里就有点不对了，com.android.providers.media.module按理也是android系统中一个重要的进程，不应该就因为拔一个U盘就重启了吧，阅读KillProcessesWithOpenFiles代码，看到有一个判断：

int KillProcessesWithOpenFiles(const std::string& prefix, int signal, bool killFuseDaemon) {...if (found) {if (!IsFuseDaemon(pid) || killFuseDaemon) {   // 判断进程是否为fusedaemonpids.insert(pid);} else {LOG(WARNING) << "Found FUSE daemon with open file. Skipping...";}}...
}// TODO: Use a better way to determine if it's media provider app.
bool IsFuseDaemon(const pid_t pid) {auto path = StringPrintf("/proc/%d/mounts", pid);char* tmp;if (lgetfilecon(path.c_str(), &tmp) < 0) {   // 这里的判断是否存在不确定性？return false;}bool result = android::base::StartsWith(tmp, kMediaProviderAppCtx)|| android::base::StartsWith(tmp, kMediaProviderCtx);freecon(tmp);return result;
}