blast: fix leak on BufferStateLayer death

SurfaceFlinger can occasionally leak graphic buffers.

The leak happens when:
1) a transaction comes in and is placed in a queue
2) Chrome crashes
3) the parent layer is cleaned up
4) the child layer is told to release its buffer because it is
        no longer on screen
5) the transaction is applied with sets a callback handle on the
        layer which has a sp<> to the layer

To fix this, the callback handle should not have a sp<> to layer.
It is safe for the callback handle can have wp<> to the layer.
The client side has a sp<> so during normal operation, SurfaceFlinger
can promote the wp<>. The only time the promote will fail is if the
client side is dead. If the client side is dead, there is no one
to send a callback to so it doesn't matter if the promote fails.

Bug: 135951943
Test: https://buganizer.corp.google.com/issues/135951943#comment34
Change-Id: I756ace14c90b03a6499a3187d235b42d91cdd05a

2 files changed, 9 insertions, 3 deletions

diff --git a/services/surfaceflinger/TransactionCompletedThread.cpp b/services/surfaceflinger/TransactionCompletedThread.cpp
index 5cf8eb1a1d..fd466dedff 100644
--- a/services/surfaceflinger/TransactionCompletedThread.cpp
+++ b/services/surfaceflinger/TransactionCompletedThread.cpp
@@ -197,8 +197,14 @@ status_t TransactionCompletedThread::addCallbackHandle(const sp<CallbackHandle>&
     }
 
     transactionStats->latchTime = handle->latchTime;
-    transactionStats->surfaceStats.emplace_back(handle->surfaceControl, handle->acquireTime,
-                                                handle->previousReleaseFence);
+    // If the layer has already been destroyed, don't add the SurfaceControl to the callback.
+    // The client side keeps a sp<> to the SurfaceControl so if the SurfaceControl has been
+    // destroyed the client side is dead and there won't be anyone to send the callback to.
+    sp<IBinder> surfaceControl = handle->surfaceControl.promote();
+    if (surfaceControl) {
+        transactionStats->surfaceStats.emplace_back(surfaceControl, handle->acquireTime,
+                                                    handle->previousReleaseFence);
+    }
     return NO_ERROR;
 }
 
diff --git a/services/surfaceflinger/TransactionCompletedThread.h b/services/surfaceflinger/TransactionCompletedThread.h
index 21e2678701..e849f714d0 100644
--- a/services/surfaceflinger/TransactionCompletedThread.h
+++ b/services/surfaceflinger/TransactionCompletedThread.h
@@ -49,7 +49,7 @@ public:
 
     sp<ITransactionCompletedListener> listener;
     std::vector<CallbackId> callbackIds;
-    sp<IBinder> surfaceControl;
+    wp<IBinder> surfaceControl;
 
     bool releasePreviousBuffer = false;
     sp<Fence> previousReleaseFence;