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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/247094">247094</a></dd>
<dt>Author</dt> <dd>cdumez@apple.com</dd>
<dt>Date</dt> <dd>2019-07-03 10:48:41 -0700 (Wed, 03 Jul 2019)</dd>
</dl>

<h3>Log Message</h3>
<pre>Crash under WTF::RefCounted<WebKit::TaskCounter>::deref()
https://bugs.webkit.org/show_bug.cgi?id=199453
<rdar://problem/51991477>

Reviewed by Youenn Fablet.

The crash was caused by StorageManager::suspend() getting called on the main thread but calling
its completion handler on a background queue. The completion handler was capturing a TaskCounter
object which is RefCounted (not ThreadSafeRefCounted).

Address the issue by making sure StorageManager::suspend() calls its completion handler on the
main thread. Also get rid of TaskCounter and use a WTF::CallbackAggregator instead.

* NetworkProcess/NetworkProcess.cpp:
(WebKit::NetworkProcess::actualPrepareToSuspend):
(WebKit::TaskCounter::TaskCounter): Deleted.
(WebKit::TaskCounter::~TaskCounter): Deleted.
* NetworkProcess/WebStorage/StorageManager.cpp:
(WebKit::StorageManager::suspend):</pre>

<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebKitChangeLog">trunk/Source/WebKit/ChangeLog</a></li>
<li><a href="#trunkSourceWebKitNetworkProcessNetworkProcesscpp">trunk/Source/WebKit/NetworkProcess/NetworkProcess.cpp</a></li>
<li><a href="#trunkSourceWebKitNetworkProcessWebStorageStorageManagercpp">trunk/Source/WebKit/NetworkProcess/WebStorage/StorageManager.cpp</a></li>
</ul>

</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebKitChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/ChangeLog (247093 => 247094)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/ChangeLog    2019-07-03 17:40:38 UTC (rev 247093)
+++ trunk/Source/WebKit/ChangeLog       2019-07-03 17:48:41 UTC (rev 247094)
</span><span class="lines">@@ -1,3 +1,25 @@
</span><ins>+2019-07-03  Chris Dumez  <cdumez@apple.com>
+
+        Crash under WTF::RefCounted<WebKit::TaskCounter>::deref()
+        https://bugs.webkit.org/show_bug.cgi?id=199453
+        <rdar://problem/51991477>
+
+        Reviewed by Youenn Fablet.
+
+        The crash was caused by StorageManager::suspend() getting called on the main thread but calling
+        its completion handler on a background queue. The completion handler was capturing a TaskCounter
+        object which is RefCounted (not ThreadSafeRefCounted).
+
+        Address the issue by making sure StorageManager::suspend() calls its completion handler on the
+        main thread. Also get rid of TaskCounter and use a WTF::CallbackAggregator instead.
+
+        * NetworkProcess/NetworkProcess.cpp:
+        (WebKit::NetworkProcess::actualPrepareToSuspend):
+        (WebKit::TaskCounter::TaskCounter): Deleted.
+        (WebKit::TaskCounter::~TaskCounter): Deleted.
+        * NetworkProcess/WebStorage/StorageManager.cpp:
+        (WebKit::StorageManager::suspend):
+
</ins><span class="cx"> 2019-07-03  Youenn Fablet  <youenn@apple.com>
</span><span class="cx"> 
</span><span class="cx">         Make sure to cross-thread copy in StorageManager when hopping back to the main thread
</span></span></pre></div>
<a id="trunkSourceWebKitNetworkProcessNetworkProcesscpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/NetworkProcess/NetworkProcess.cpp (247093 => 247094)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/NetworkProcess/NetworkProcess.cpp    2019-07-03 17:40:38 UTC (rev 247093)
+++ trunk/Source/WebKit/NetworkProcess/NetworkProcess.cpp       2019-07-03 17:48:41 UTC (rev 247094)
</span><span class="lines">@@ -2029,16 +2029,6 @@
</span><span class="cx">     platformProcessDidTransitionToBackground();
</span><span class="cx"> }
</span><span class="cx"> 
</span><del>-// FIXME: We can remove this one by adapting RefCounter.
-class TaskCounter : public RefCounted<TaskCounter> {
-public:
-    explicit TaskCounter(Function<void()>&& callback) : m_callback(WTFMove(callback)) { }
-    ~TaskCounter() { m_callback(); };
-
-private:
-    Function<void()> m_callback;
-};
-
</del><span class="cx"> void NetworkProcess::actualPrepareToSuspend(ShouldAcknowledgeWhenReadyToSuspend shouldAcknowledgeWhenReadyToSuspend)
</span><span class="cx"> {
</span><span class="cx"> #if PLATFORM(IOS_FAMILY)
</span><span class="lines">@@ -2047,30 +2037,30 @@
</span><span class="cx"> 
</span><span class="cx">     lowMemoryHandler(Critical::Yes);
</span><span class="cx"> 
</span><del>-    RefPtr<TaskCounter> delayedTaskCounter;
</del><ins>+    RefPtr<CallbackAggregator> callbackAggregator;
</ins><span class="cx">     if (shouldAcknowledgeWhenReadyToSuspend == ShouldAcknowledgeWhenReadyToSuspend::Yes) {
</span><del>-        delayedTaskCounter = adoptRef(new TaskCounter([this] {
</del><ins>+        callbackAggregator = CallbackAggregator::create([this] {
</ins><span class="cx">             RELEASE_LOG(ProcessSuspension, "%p - NetworkProcess::notifyProcessReadyToSuspend() Sending ProcessReadyToSuspend IPC message", this);
</span><span class="cx">             if (parentProcessConnection())
</span><span class="cx">                 parentProcessConnection()->send(Messages::NetworkProcessProxy::ProcessReadyToSuspend(), 0);
</span><del>-        }));
</del><ins>+        });
</ins><span class="cx">     }
</span><span class="cx"> 
</span><del>-    platformPrepareToSuspend([delayedTaskCounter] { });
-    platformSyncAllCookies([delayedTaskCounter] { });
</del><ins>+    platformPrepareToSuspend([callbackAggregator] { });
+    platformSyncAllCookies([callbackAggregator] { });
</ins><span class="cx"> 
</span><span class="cx">     for (auto& connection : m_webProcessConnections)
</span><del>-        connection->cleanupForSuspension([delayedTaskCounter] { });
</del><ins>+        connection->cleanupForSuspension([callbackAggregator] { });
</ins><span class="cx"> 
</span><span class="cx"> #if ENABLE(SERVICE_WORKER)
</span><span class="cx">     for (auto& server : m_swServers.values()) {
</span><span class="cx">         ASSERT(m_swServers.get(server->sessionID()) == server.get());
</span><del>-        server->startSuspension([delayedTaskCounter] { });
</del><ins>+        server->startSuspension([callbackAggregator] { });
</ins><span class="cx">     }
</span><span class="cx"> #endif
</span><span class="cx"> 
</span><span class="cx">     for (auto& session : m_networkSessions)
</span><del>-        session.value->storageManager().suspend([delayedTaskCounter] { });
</del><ins>+        session.value->storageManager().suspend([callbackAggregator] { });
</ins><span class="cx"> }
</span><span class="cx"> 
</span><span class="cx"> void NetworkProcess::processWillSuspendImminently()
</span></span></pre></div>
<a id="trunkSourceWebKitNetworkProcessWebStorageStorageManagercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebKit/NetworkProcess/WebStorage/StorageManager.cpp (247093 => 247094)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebKit/NetworkProcess/WebStorage/StorageManager.cpp 2019-07-03 17:40:38 UTC (rev 247093)
+++ trunk/Source/WebKit/NetworkProcess/WebStorage/StorageManager.cpp    2019-07-03 17:48:41 UTC (rev 247094)
</span><span class="lines">@@ -936,11 +936,14 @@
</span><span class="cx">         Locker<Lock> stateLocker(m_stateLock);
</span><span class="cx">         ASSERT(m_state != State::Suspended);
</span><span class="cx"> 
</span><del>-        completionHandler();
</del><ins>+        if (m_state != State::WillSuspend) {
+            RunLoop::main().dispatch(WTFMove(completionHandler));
+            return;
+        }
</ins><span class="cx"> 
</span><del>-        if (m_state != State::WillSuspend)
-            return;
</del><span class="cx">         m_state = State::Suspended;
</span><ins>+        RunLoop::main().dispatch(WTFMove(completionHandler));
+        
</ins><span class="cx">         while (m_state == State::Suspended)
</span><span class="cx">             m_stateChangeCondition.wait(m_stateLock);
</span><span class="cx">         ASSERT(m_state == State::Running);
</span></span></pre>
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