From 51e4dc89f0e9b93f0be3204181caa9bef5376746 Mon Sep 17 00:00:00 2001
From: Vishnu Nair <vishnun@google.com>
Date: Fri, 1 Oct 2021 15:32:33 -0700
Subject: BlastBufferQueue: Fix async worker deadlock

The async onBufferReleased callback can trigger another
onBufferReleased which will end up deadlocking the
async worker thread. Fix this by executing the callbacks
outside the lock.

Test: atest android.media.cts.MediaSyncTest#testPlaybackRateDouble --rerun-util-failure 100
Fixes: 201604213
Change-Id: I40d163c3644c6a0128936cf41e8bf8969766d9da
---
 libs/gui/BLASTBufferQueue.cpp | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

(limited to 'libs/gui/BLASTBufferQueue.cpp')

diff --git a/libs/gui/BLASTBufferQueue.cpp b/libs/gui/BLASTBufferQueue.cpp
index d1f57b03bc..5b9d912723 100644
--- a/libs/gui/BLASTBufferQueue.cpp
+++ b/libs/gui/BLASTBufferQueue.cpp
@@ -738,14 +738,26 @@ private:
         std::unique_lock<std::mutex> lock(mMutex);
         while (!mDone) {
             while (!mRunnables.empty()) {
-                std::function<void()> runnable = mRunnables.front();
-                mRunnables.pop_front();
-                runnable();
+                std::deque<std::function<void()>> runnables = std::move(mRunnables);
+                mRunnables.clear();
+                lock.unlock();
+                // Run outside the lock since the runnable might trigger another
+                // post to the async worker.
+                execute(runnables);
+                lock.lock();
             }
             mCv.wait(lock);
         }
     }
 
+    void execute(std::deque<std::function<void()>>& runnables) {
+        while (!runnables.empty()) {
+            std::function<void()> runnable = runnables.front();
+            runnables.pop_front();
+            runnable();
+        }
+    }
+
 public:
     AsyncWorker() : Singleton<AsyncWorker>() { mThread = std::thread(&AsyncWorker::run, this); }
 
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