UserAwareBiometricScheduler lifecycle fix.

Fixed an issue where UserAwareBiometricScheduler queue would get stuck
indefinitely(causing face/fingerprint to fail until reboot).

Testing steps to reproduce

Setup.
* Have multiple users with multipler biometrics.

1. Add a property in a biometric HAL(Call it biometric A) to hang on auth operation
2. Set property to hang when authenticating(biometric A).
3. Unlock device with alternative biometric(biometric B)/pin/pattern/pass
4. Unset property to stop biometric(biometric A) from hanging
5. Rinse and repeat 1-4 until a hang occurs

Test: Manual (See above)
Test: atest UserAwareBiometricSchedulerTest
Fixes: 234625004
Change-Id: Ia6055ef3314ddaf986d5dfb4b642a5aba183053d

services/core/java/com/android/server/biometrics/sensors/UserAwareBiometricScheduler.java

@@ -67,6 +67,14 @@ public class UserAwareBiometricScheduler extends BiometricScheduler {
         public void onClientFinished(@NonNull BaseClientMonitor clientMonitor, boolean success) {
             mHandler.post(() -> {
                 Slog.d(getTag(), "[Client finished] " + clientMonitor + ", success: " + success);
+
+                // Set mStopUserClient to null when StopUserClient fails. Otherwise it's possible
+                // for that the queue will wait indefinitely until the field is cleared.
+                if (clientMonitor instanceof StopUserClient<?> && !success) {
+                    Slog.w(getTag(),
+                            "StopUserClient failed(), is the HAL stuck? Clearing mStopUserClient");
+                    mStopUserClient = null;
+                }
                 if (mCurrentOperation != null && mCurrentOperation.isFor(mOwner)) {
                     mCurrentOperation = null;
                 } else {
@@ -166,4 +174,9 @@ public class UserAwareBiometricScheduler extends BiometricScheduler {
         mStopUserClient.onUserStopped();
         mStopUserClient = null;
     }
+
+    @VisibleForTesting
+    @Nullable public StopUserClient<?> getStopUserClient() {
+        return mStopUserClient;
+    }
 }

services/tests/servicestests/src/com/android/server/biometrics/sensors/UserAwareBiometricSchedulerTest.java

@@ -80,6 +80,11 @@ public class UserAwareBiometricSchedulerTest {
     @Mock
     private BiometricContext mBiometricContext;
 
+    private boolean mShouldFailStopUser = false;
+    private final StopUserClientShouldFail mStopUserClientShouldFail =
+            () -> {
+                return mShouldFailStopUser;
+            };
     private final TestUserStartedCallback mUserStartedCallback = new TestUserStartedCallback();
     private final TestUserStoppedCallback mUserStoppedCallback = new TestUserStoppedCallback();
     private int mCurrentUserId = UserHandle.USER_NULL;
@@ -88,6 +93,7 @@ public class UserAwareBiometricSchedulerTest {
 
     @Before
     public void setUp() {
+        mShouldFailStopUser = false;
         mHandler = new Handler(TestableLooper.get(this).getLooper());
         mScheduler = new UserAwareBiometricScheduler(TAG,
                 mHandler,
@@ -101,7 +107,7 @@ public class UserAwareBiometricSchedulerTest {
                     public StopUserClient<?> getStopUserClient(int userId) {
                         return new TestStopUserClient(mContext, Object::new, mToken, userId,
                                 TEST_SENSOR_ID, mBiometricLogger, mBiometricContext,
-                                mUserStoppedCallback);
+                                mUserStoppedCallback, mStopUserClientShouldFail);
                     }
 
                     @NonNull
@@ -240,6 +246,36 @@ public class UserAwareBiometricSchedulerTest {
         assertThat(mUserStoppedCallback.mNumInvocations).isEqualTo(1);
     }
 
+    @Test
+    public void testStartUser_failsClearsStopUserClient() {
+        // When a stop user client fails, check that mStopUserClient
+        // is set to null to prevent the scheduler from getting stuck.
+        BaseClientMonitor nextClient = mock(BaseClientMonitor.class);
+        when(nextClient.getTargetUserId()).thenReturn(10);
+
+        mScheduler.scheduleClientMonitor(nextClient);
+
+        waitForIdle();
+        verify(nextClient).start(any());
+
+        // finish first operation
+        mScheduler.getInternalCallback().onClientFinished(nextClient, true /* success */);
+        waitForIdle();
+
+        // schedule second operation but swap out the current operation
+        // before it runs so that it's not current when it's completion callback runs
+        nextClient = mock(BaseClientMonitor.class);
+        when(nextClient.getTargetUserId()).thenReturn(11);
+        mUserStartedCallback.mAfterStart = () -> mScheduler.mCurrentOperation = null;
+        mShouldFailStopUser = true;
+        mScheduler.scheduleClientMonitor(nextClient);
+
+        waitForIdle();
+        assertThat(mUserStartedCallback.mStartedUsers).containsExactly(10, 11).inOrder();
+        assertThat(mUserStoppedCallback.mNumInvocations).isEqualTo(0);
+        assertThat(mScheduler.getStopUserClient()).isEqualTo(null);
+    }
+
     private void waitForIdle() {
         TestableLooper.get(this).processAllMessages();
     }
@@ -268,13 +304,19 @@ public class UserAwareBiometricSchedulerTest {
         }
     }
 
-    private static class TestStopUserClient extends StopUserClient<Object> {
+    private interface StopUserClientShouldFail {
+        boolean shouldFail();
+    }
+
+    private class TestStopUserClient extends StopUserClient<Object> {
+        private StopUserClientShouldFail mShouldFailClient;
         public TestStopUserClient(@NonNull Context context,
                 @NonNull Supplier<Object> lazyDaemon, @Nullable IBinder token, int userId,
                 int sensorId, @NonNull BiometricLogger logger,
                 @NonNull BiometricContext biometricContext,
-                @NonNull UserStoppedCallback callback) {
+                @NonNull UserStoppedCallback callback, StopUserClientShouldFail shouldFail) {
             super(context, lazyDaemon, token, userId, sensorId, logger, biometricContext, callback);
+            mShouldFailClient = shouldFail;
         }
 
         @Override
@@ -285,7 +327,14 @@ public class UserAwareBiometricSchedulerTest {
         @Override
         public void start(@NonNull ClientMonitorCallback callback) {
             super.start(callback);
-            onUserStopped();
+            if (mShouldFailClient.shouldFail()) {
+                getCallback().onClientFinished(this, false /* success */);
+                // When the above fails, it means that the HAL has died, in this case we
+                // need to ensure the UserSwitchCallback correctly returns the NULL user handle.
+                mCurrentUserId = UserHandle.USER_NULL;
+            } else {
+                onUserStopped();
+            }
         }
 
         @Override