前言

之前專案，一直會出現剛開機就出現“正在關機”對話框，然后就關機了，通過串口看內核log，發現進入了recovery模式，然后就跟了一下代碼，看什么情況下會進入這個模式

代碼分析

關機對話框

關機對話框顯示在
frameworks/base/services/core/java/com/android/server/power/ShutdownThread.java

而呼叫者在
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java

    private void shutdownOrRebootInternal(final @HaltMode int haltMode, final boolean confirm,
            final String reason, boolean wait) {
        if (mHandler == null || !mSystemReady) {
            if (RescueParty.isAttemptingFactoryReset()) {
                // If we're stuck in a really low-level reboot loop, and a
                // rescue party is trying to prompt the user for a factory data
                // reset, we must GET TO DA CHOPPA!
                PowerManagerService.lowLevelReboot(reason);
            } else {
                throw new IllegalStateException("Too early to call shutdown() or reboot()");
            }
        }

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                synchronized (this) {
                    if (haltMode == HALT_MODE_REBOOT_SAFE_MODE) {
                        ShutdownThread.rebootSafeMode(getUiContext(), confirm);
                    } else if (haltMode == HALT_MODE_REBOOT) {
                        ShutdownThread.reboot(getUiContext(), reason, confirm);
                    } else {
                        ShutdownThread.shutdown(getUiContext(), reason, confirm);
                    }
                }
            }
        };
......
}

lowLevelReboot往下看,就很簡單，只是設定了一個properties，然后init 行程會handle這個prop行程關機動作

    public static void lowLevelReboot(String reason) {
        if (reason == null) {
            reason = "";
        }

        // If the reason is "quiescent", it means that the boot process should proceed
        // without turning on the screen/lights.
        // The "quiescent" property is sticky, meaning that any number
        // of subsequent reboots should honor the property until it is reset.
        if (reason.equals(PowerManager.REBOOT_QUIESCENT)) {
            sQuiescent = true;
            reason = "";
        } else if (reason.endsWith("," + PowerManager.REBOOT_QUIESCENT)) {
            sQuiescent = true;
            reason = reason.substring(0,
                    reason.length() - PowerManager.REBOOT_QUIESCENT.length() - 1);
        }

        if (reason.equals(PowerManager.REBOOT_RECOVERY)
                || reason.equals(PowerManager.REBOOT_RECOVERY_UPDATE)) {
            reason = "recovery";
        }

        if (sQuiescent) {
            // Pass the optional "quiescent" argument to the bootloader to let it know
            // that it should not turn the screen/lights on.
            reason = reason + ",quiescent";
        }

        SystemProperties.set("sys.powerctl", "reboot," + reason);
        try {
            Thread.sleep(20 * 1000L);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        Slog.wtf(TAG, "Unexpected return from lowLevelReboot!");
    }

        @Override // Binder call
        public void reboot(boolean confirm, String reason, boolean wait) {
            mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);
            if (PowerManager.REBOOT_RECOVERY.equals(reason)
                    || PowerManager.REBOOT_RECOVERY_UPDATE.equals(reason)) {
                mContext.enforceCallingOrSelfPermission(android.Manifest.permission.RECOVERY, null);
            }

            final long ident = Binder.clearCallingIdentity();
            try {
                shutdownOrRebootInternal(HALT_MODE_REBOOT, confirm, reason, wait);
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }

frameworks/base/services/core/java/com/android/server/RecoverySystemService.java

        @Override // Binder call
        public void rebootRecoveryWithCommand(String command) {
            if (DEBUG) Slog.d(TAG, "rebootRecoveryWithCommand: [" + command + "]");
            synchronized (sRequestLock) {
                if (!setupOrClearBcb(true, command)) {
                    return;
                }

                // Having set up the BCB, go ahead and reboot.
                PowerManager pm = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
                pm.reboot(PowerManager.REBOOT_RECOVERY);
            }
        }

frameworks/base/core/java/android/os/RecoverySystem.java

    private void rebootRecoveryWithCommand(String command) {
        try {
            mService.rebootRecoveryWithCommand(command);
        } catch (RemoteException ignored) {
        }
    }

    private static void bootCommand(Context context, String... args) throws IOException {
        LOG_FILE.delete();

        StringBuilder command = new StringBuilder();
        for (String arg : args) {
            if (!TextUtils.isEmpty(arg)) {
                command.append(arg);
                command.append("\n");
            }
        }

        // Write the command into BCB (bootloader control block) and boot from
        // there. Will not return unless failed.
        RecoverySystem rs = (RecoverySystem) context.getSystemService(Context.RECOVERY_SERVICE);
        rs.rebootRecoveryWithCommand(command.toString());

        throw new IOException("Reboot failed (no permissions?)");
    }

    public static void rebootPromptAndWipeUserData(Context context, String reason)
            throws IOException {
        String reasonArg = null;
        if (!TextUtils.isEmpty(reason)) {
            reasonArg = "--reason=" + sanitizeArg(reason);
        }

        final String localeArg = "--locale=" + Locale.getDefault().toString();
        bootCommand(context, null, "--prompt_and_wipe_data", reasonArg, localeArg);
    }

frameworks/base/services/core/java/com/android/server/RescueParty.java

    private static void executeRescueLevelInternal(Context context, int level) throws Exception {
        switch (level) {
            case LEVEL_RESET_SETTINGS_UNTRUSTED_DEFAULTS:
                resetAllSettings(context, Settings.RESET_MODE_UNTRUSTED_DEFAULTS);
                break;
            case LEVEL_RESET_SETTINGS_UNTRUSTED_CHANGES:
                resetAllSettings(context, Settings.RESET_MODE_UNTRUSTED_CHANGES);
                break;
            case LEVEL_RESET_SETTINGS_TRUSTED_DEFAULTS:
                resetAllSettings(context, Settings.RESET_MODE_TRUSTED_DEFAULTS);
                break;
            case LEVEL_FACTORY_RESET:
                RecoverySystem.rebootPromptAndWipeUserData(context, TAG);
                break;
        }
    }

    private static void executeRescueLevel(Context context) {
        final int level = SystemProperties.getInt(PROP_RESCUE_LEVEL, LEVEL_NONE);
        if (level == LEVEL_NONE) return;

        Slog.w(TAG, "Attempting rescue level " + levelToString(level));
        try {
            executeRescueLevelInternal(context, level);
            EventLogTags.writeRescueSuccess(level);
            logCriticalInfo(Log.DEBUG,
                    "Finished rescue level " + levelToString(level));
        } catch (Throwable t) {
            final String msg = ExceptionUtils.getCompleteMessage(t);
            EventLogTags.writeRescueFailure(level, msg);
            logCriticalInfo(Log.ERROR,
                    "Failed rescue level " + levelToString(level) + ": " + msg);
        }
    }

    public static void notePersistentAppCrash(Context context, int uid) {
        if (isDisabled()) return;
        Threshold t = sApps.get(uid);
        if (t == null) {
            t = new AppThreshold(uid);
            sApps.put(uid, t);
        }
        if (t.incrementAndTest()) {
            t.reset();
            incrementRescueLevel(t.uid);
            executeRescueLevel(context);
        }
    }

    /**
     * Specialization of {@link Threshold} for monitoring app crashes. It stores
     * counters in memory.
     */
    private static class AppThreshold extends Threshold {
        private int count;
        private long start;

        public AppThreshold(int uid) {
            // We're interested in 5 events in any 30 second period; apps crash
            // pretty quickly so we can keep a tight leash on them.
            super(uid, 5, 30 * DateUtils.SECOND_IN_MILLIS);
        }

        @Override public int getCount() { return count; }
        @Override public void setCount(int count) { this.count = count; }
        @Override public long getStart() { return start; }
        @Override public void setStart(long start) { this.start = start; }
    }

    private static void incrementRescueLevel(int triggerUid) {
        final int level = MathUtils.constrain(
                SystemProperties.getInt(PROP_RESCUE_LEVEL, LEVEL_NONE) + 1,
                LEVEL_NONE, LEVEL_FACTORY_RESET);
        SystemProperties.set(PROP_RESCUE_LEVEL, Integer.toString(level));

        EventLogTags.writeRescueLevel(level, triggerUid);
        logCriticalInfo(Log.WARN, "Incremented rescue level to "
                + levelToString(level) + " triggered by UID " + triggerUid);
    }

frameworks/base/services/core/java/com/android/server/am/AppErrors.java

    void crashApplicationInner(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo,
            int callingPid, int callingUid) {
        long timeMillis = System.currentTimeMillis();
        String shortMsg = crashInfo.exceptionClassName;
        String longMsg = crashInfo.exceptionMessage;
        String stackTrace = crashInfo.stackTrace;
        if (shortMsg != null && longMsg != null) {
            longMsg = shortMsg + ": " + longMsg;
        } else if (shortMsg != null) {
            longMsg = shortMsg;
        }

        // If a persistent app is stuck in a crash loop, the device isn't very
        // usable, so we want to consider sending out a rescue party.
        if (r != null && r.persistent) {
            RescueParty.notePersistentAppCrash(mContext, r.uid);
        }
        ......

    void crashApplication(ProcessRecord r, ApplicationErrorReport.CrashInfo crashInfo) {
        final int callingPid = Binder.getCallingPid();
        final int callingUid = Binder.getCallingUid();

        final long origId = Binder.clearCallingIdentity();
        try {
            crashApplicationInner(r, crashInfo, callingPid, callingUid);
        } finally {
            Binder.restoreCallingIdentity(origId);
        }
    }

frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java

    /**
     * Used by {@link com.android.internal.os.RuntimeInit} to report when an application crashes.
     * The application process will exit immediately after this call returns.
     * @param app object of the crashing app, null for the system server
     * @param crashInfo describing the exception
     */
    public void handleApplicationCrash(IBinder app,
            ApplicationErrorReport.ParcelableCrashInfo crashInfo) {
        ProcessRecord r = findAppProcess(app, "Crash");
        final String processName = app == null ? "system_server"
                : (r == null ? "unknown" : r.processName);

        handleApplicationCrashInner("crash", r, processName, crashInfo);
    }

    /* Native crash reporting uses this inner version because it needs to be somewhat
     * decoupled from the AM-managed cleanup lifecycle
     */
    void handleApplicationCrashInner(String eventType, ProcessRecord r, String processName,
            ApplicationErrorReport.CrashInfo crashInfo) {
        EventLog.writeEvent(EventLogTags.AM_CRASH, Binder.getCallingPid(),
                UserHandle.getUserId(Binder.getCallingUid()), processName,
                r == null ? -1 : r.info.flags,
                crashInfo.exceptionClassName,
                crashInfo.exceptionMessage,
                crashInfo.throwFileName,
                crashInfo.throwLineNumber);

        StatsLog.write(StatsLog.APP_CRASH_OCCURRED,
                Binder.getCallingUid(),
                eventType,
                processName,
                Binder.getCallingPid(),
                (r != null && r.info != null) ? r.info.packageName : "",
                (r != null && r.info != null) ? (r.info.isInstantApp()
                        ? StatsLog.APP_CRASH_OCCURRED__IS_INSTANT_APP__TRUE
                        : StatsLog.APP_CRASH_OCCURRED__IS_INSTANT_APP__FALSE)
                        : StatsLog.APP_CRASH_OCCURRED__IS_INSTANT_APP__UNAVAILABLE,
                r != null ? (r.isInterestingToUserLocked()
                        ? StatsLog.APP_CRASH_OCCURRED__FOREGROUND_STATE__FOREGROUND
                        : StatsLog.APP_CRASH_OCCURRED__FOREGROUND_STATE__BACKGROUND)
                        : StatsLog.APP_CRASH_OCCURRED__FOREGROUND_STATE__UNKNOWN
        );

        addErrorToDropBox(eventType, r, processName, null, null, null, null, null, crashInfo);

        mAppErrors.crashApplication(r, crashInfo);
    }

總結

到這里就可以知道使用一個persistent的APP連續4次在30S內crash 5次就是觸發重啟到recovery模式