Fix deadlock on QWebEngineUrlRequestJob::fail

URLRequestCustomJob::notifyFailure calls NotifyStartError(status), which
in turn will result in a call to URLRequestCustomJob::Kill.
We must release the lock of m_mutex before calling NotifyStartError,
otherwise m_mutex.lock() will wait forever in Kill.

Change-Id: I319e45049766c2192dfc46a91b352b92ec677bc6
Task-number: QTBUG-50160
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/core/url_request_custom_job.cpp b/src/core/url_request_custom_job.cpp
index 1b6f1c767..907f71c2e 100644
--- a/src/core/url_request_custom_job.cpp
+++ b/src/core/url_request_custom_job.cpp
@@ -222,13 +222,17 @@ void URLRequestCustomJob::fail(int error)
 void URLRequestCustomJob::notifyFailure()
 {
     DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
-    QMutexLocker lock(&m_mutex);
+    m_mutex.lock();
     if (m_device)
         m_device->close();
-    if (m_started)
-        NotifyDone(URLRequestStatus(URLRequestStatus::FAILED, m_error));
+    const URLRequestStatus status(URLRequestStatus::FAILED, m_error);
+    const bool started = m_started;
+    m_mutex.unlock();
+
+    if (started)
+        NotifyDone(status);
     else
-        NotifyStartError(URLRequestStatus(URLRequestStatus::FAILED, m_error));
+        NotifyStartError(status);
 }
 
 void URLRequestCustomJob::startAsync()