Serialize AM.getContentProvider() calls in client side

Th wait() call in AMS.getContentProviderImpl() can cause a deadlock when it
starts a new process for a target provider and all system server binder threads
are reaching out to the same provider at the same time, because AMS won't be
able to receive a callback from the provider process.

Let's serialize access to AM.getContentProvider() to avoid this scenario.

Longer team, we should stop waiting in the system server and instead do so in
the client side.

Bug: 74523247
Test: Boot, add a google account, and let syncs run and finish.
Test: Watch free video on Coursera

Change-Id: If5be2dc4b6f22f72d1bb3aa1b5b4d49f20c8d94d

core/java/android/app/ActivityThread.java

@@ -347,6 +347,13 @@ public final class ActivityThread extends ClientTransactionHandler {
     final ArrayMap<ComponentName, ProviderClientRecord> mLocalProvidersByName
             = new ArrayMap<ComponentName, ProviderClientRecord>();
 
+    // Mitigation for b/74523247: Used to serialize calls to AM.getContentProvider().
+    // Note we never removes items from this map but that's okay because there are only so many
+    // users and so many authorities.
+    // TODO Remove it once we move CPR.wait() from AMS to the client side.
+    @GuardedBy("mGetProviderLocks")
+    final ArrayMap<ProviderKey, Object> mGetProviderLocks = new ArrayMap<>();
+
     final ArrayMap<Activity, ArrayList<OnActivityPausedListener>> mOnPauseListeners
         = new ArrayMap<Activity, ArrayList<OnActivityPausedListener>>();
 
@@ -5959,8 +5966,10 @@ public final class ActivityThread extends ClientTransactionHandler {
         // be re-entrant in the case where the provider is in the same process.
         ContentProviderHolder holder = null;
         try {
-            holder = ActivityManager.getService().getContentProvider(
-                    getApplicationThread(), auth, userId, stable);
+            synchronized (getGetProviderLock(auth, userId)) {
+                holder = ActivityManager.getService().getContentProvider(
+                        getApplicationThread(), auth, userId, stable);
+            }
         } catch (RemoteException ex) {
             throw ex.rethrowFromSystemServer();
         }
@@ -5976,6 +5985,18 @@ public final class ActivityThread extends ClientTransactionHandler {
         return holder.provider;
     }
 
+    private Object getGetProviderLock(String auth, int userId) {
+        final ProviderKey key = new ProviderKey(auth, userId);
+        synchronized (mGetProviderLocks) {
+            Object lock = mGetProviderLocks.get(key);
+            if (lock == null) {
+                lock = key;
+                mGetProviderLocks.put(key, lock);
+            }
+            return lock;
+        }
+    }
+
     private final void incProviderRefLocked(ProviderRefCount prc, boolean stable) {
         if (stable) {
             prc.stableCount += 1;