cherry-pick-72ee7c437c88.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Fri, 7 Aug 2020 15:27:06 +0000
Subject: Worker: Fix a race condition on task runner handling

WebSharedWorkerImpl accesses WorkerScheduler from the main thread to
take a task runner, and then dispatches a connect event to
SharedWorkerGlobalScope using the task runner.

This causes a race condition if close() is called on the global scope
on the worker thread while the task runner is being taken on the main
thread: close() call disposes of WorkerScheduler, and accessing the
scheduler after that is not allowed. See the issue for details.

To fix this, this CL makes WebSharedWorkerImpl capture the task runner
between starting a worker thread (initializing WorkerScheduler) and
posting a task to evaluate worker scripts that may call close(). This
ensures that WebSharedWorkerImpl accesses WorkerScheduler before the
scheduler is disposed of.

(cherry picked from commit c7bbec3e595c4359e36e5472b7265c4b6d047f2c)

Bug: 1104046
Change-Id: I145cd39f706019c33220fcb01ed81f76963ffff0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2308550
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#790284}
Tbr: bashi@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2342337
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/branch-heads/4147@{#1050}
Cr-Branched-From: 16307825352720ae04d898f37efa5449ad68b606-refs/heads/master@{#768962}

diff --git a/third_party/blink/renderer/core/exported/web_shared_worker_impl.cc b/third_party/blink/renderer/core/exported/web_shared_worker_impl.cc
index aa09f9c3cc442428830b7b6ef9d569f3da1e5269..4c62f91873619cdf85b95125e7391d6be330fecd 100644
--- a/third_party/blink/renderer/core/exported/web_shared_worker_impl.cc
+++ b/third_party/blink/renderer/core/exported/web_shared_worker_impl.cc
@@ -129,11 +129,8 @@ void WebSharedWorkerImpl::Connect(MessagePortChannel web_channel) {
   DCHECK(IsMainThread());
   if (asked_to_terminate_)
     return;
-  // The HTML spec requires to queue a connect event using the DOM manipulation
-  // task source.
-  // https://html.spec.whatwg.org/C/#shared-workers-and-the-sharedworker-interface
   PostCrossThreadTask(
-      *GetWorkerThread()->GetTaskRunner(TaskType::kDOMManipulation), FROM_HERE,
+      *task_runner_for_connect_event_, FROM_HERE,
       CrossThreadBindOnce(&WebSharedWorkerImpl::ConnectTaskOnWorkerThread,
                           WTF::CrossThreadUnretained(this),
                           WTF::Passed(std::move(web_channel))));
@@ -248,6 +245,18 @@ void WebSharedWorkerImpl::StartWorkerContext(
 
   GetWorkerThread()->Start(std::move(creation_params), thread_startup_data,
                            std::move(devtools_params));
+
+  // Capture the task runner for dispatching connect events. This is necessary
+  // for avoiding race condition with WorkerScheduler termination induced by
+  // close() call on SharedWorkerGlobalScope. See https://crbug.com/1104046 for
+  // details.
+  //
+  // The HTML spec requires to queue a connect event using the DOM manipulation
+  // task source.
+  // https://html.spec.whatwg.org/C/#shared-workers-and-the-sharedworker-interface
+  task_runner_for_connect_event_ =
+      GetWorkerThread()->GetTaskRunner(TaskType::kDOMManipulation);
+
   GetWorkerThread()->FetchAndRunClassicScript(
       script_request_url, outside_settings_object->CopyData(),
       nullptr /* outside_resource_timing_notifier */,
diff --git a/third_party/blink/renderer/core/exported/web_shared_worker_impl.h b/third_party/blink/renderer/core/exported/web_shared_worker_impl.h
index 2c732995531f51e646808639c562eabd765ebd9f..52e0413ccfc0d6b8251b3bd13f5af11c9f1c117a 100644
--- a/third_party/blink/renderer/core/exported/web_shared_worker_impl.h
+++ b/third_party/blink/renderer/core/exported/web_shared_worker_impl.h
@@ -103,6 +103,8 @@ class CORE_EXPORT WebSharedWorkerImpl final : public WebSharedWorker {
   // |client_| owns |this|.
   WebSharedWorkerClient* client_;
 
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_for_connect_event_;
+
   bool asked_to_terminate_ = false;
 
   base::WeakPtrFactory<WebSharedWorkerImpl> weak_ptr_factory_{this};