Fix deadlock in StagingManager.getSessions() method

When we stage a session we acquire the PackageInstallerSession#mLock
first and then StagingManager#mStagedSessions lock. But in getSessions()
method, we acquire the locks in reverse order which can lead to
deadlock: we first acquire StagingManager#mStagedSessions in
getSessions() and then while checking if session is destroyed, we
acquire PackageInstallerSession#mLock in isDestroyed() method.

By moving the staged session retrieval logic to PackageInstallerService,
we avoid acquiring the StagingManager#mStagedSession lock. This avoids
deadlock.

Bug: 160113544
Test: atest StagedInstallTest
Change-Id: I7a1abf44db27d4673d43e9b0886610a5bd8b41f6
Merged-In: I7a1abf44db27d4673d43e9b0886610a5bd8b41f6
(cherry picked from commit c45b6a146c)

services/core/java/com/android/server/pm/PackageInstallerService.java

@@ -865,7 +865,16 @@ public class PackageInstallerService extends IPackageInstaller.Stub implements
 
     @Override
     public ParceledListSlice<SessionInfo> getStagedSessions() {
-        return mStagingManager.getSessions(Binder.getCallingUid());
+        final List<SessionInfo> result = new ArrayList<>();
+        synchronized (mSessions) {
+            for (int i = 0; i < mSessions.size(); i++) {
+                final PackageInstallerSession session = mSessions.valueAt(i);
+                if (session.isStaged() && !session.isDestroyed()) {
+                    result.add(session.generateInfoForCaller(false, Binder.getCallingUid()));
+                }
+            }
+        }
+        return new ParceledListSlice<>(result);
     }
 
     @Override

services/core/java/com/android/server/pm/StagingManager.java

@@ -38,7 +38,6 @@ import android.content.pm.PackageManagerInternal;
 import android.content.pm.PackageParser.PackageParserException;
 import android.content.pm.PackageParser.SigningDetails;
 import android.content.pm.PackageParser.SigningDetails.SignatureSchemeVersion;
-import android.content.pm.ParceledListSlice;
 import android.content.pm.parsing.PackageInfoWithoutStateUtils;
 import android.content.rollback.IRollbackManager;
 import android.content.rollback.RollbackInfo;
@@ -180,20 +179,6 @@ public class StagingManager {
         }
     }
 
-    ParceledListSlice<PackageInstaller.SessionInfo> getSessions(int callingUid) {
-        final List<PackageInstaller.SessionInfo> result = new ArrayList<>();
-        synchronized (mStagedSessions) {
-            for (int i = 0; i < mStagedSessions.size(); i++) {
-                final PackageInstallerSession stagedSession = mStagedSessions.valueAt(i);
-                if (stagedSession.isDestroyed()) {
-                    continue;
-                }
-                result.add(stagedSession.generateInfoForCaller(false /*icon*/, callingUid));
-            }
-        }
-        return new ParceledListSlice<>(result);
-    }
-
     /**
      * Validates the signature used to sign the container of the new apex package
      *