QTlsBackendOpenSSL: Early return from ensureCiphersAndCertsLoaded()

Add an atomic state variable to perform early return without taking
a recursive lock after ensureCiphersAndCertsLoaded() is complete.

Make related mutex and state variable function-local static because
they are not used anywhere else.

Taks-number: QTBUG-103559
Change-Id: I1e4c9c4f73204885bce82ba7f2b5e64548c3aac3
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 16 insertions, 7 deletions

diff --git a/src/plugins/tls/openssl/qtlsbackend_openssl.cpp b/src/plugins/tls/openssl/qtlsbackend_openssl.cpp
index b454a20f2a..dfd48e01af 100644
--- a/src/plugins/tls/openssl/qtlsbackend_openssl.cpp
+++ b/src/plugins/tls/openssl/qtlsbackend_openssl.cpp
@@ -33,8 +33,6 @@ using namespace Qt::StringLiterals;
 
 Q_LOGGING_CATEGORY(lcTlsBackend, "qt.tlsbackend.ossl");
 
-Q_GLOBAL_STATIC(QRecursiveMutex, qt_opensslInitMutex)
-
 static void q_loadCiphersForConnection(SSL *connection, QList<QSslCipher> &ciphers,
                                        QList<QSslCipher> &defaultCiphers)
 {
@@ -59,7 +57,6 @@ static void q_loadCiphersForConnection(SSL *connection, QList<QSslCipher> &ciphe
     }
 }
 
-bool QTlsBackendOpenSSL::s_loadedCiphersAndCerts = false;
 int QTlsBackendOpenSSL::s_indexForSSLExtraData = -1;
 
 QString QTlsBackendOpenSSL::getErrorsFromOpenSsl()
@@ -172,11 +169,24 @@ void QTlsBackendOpenSSL::ensureInitialized() const
 
 void QTlsBackendOpenSSL::ensureCiphersAndCertsLoaded() const
 {
-    const QMutexLocker locker(qt_opensslInitMutex());
+    Q_CONSTINIT static bool initializationStarted = false;
+    Q_CONSTINIT static QAtomicInt initialized = Q_BASIC_ATOMIC_INITIALIZER(0);
+    Q_CONSTINIT static QRecursiveMutex initMutex;
+
+    if (initialized.loadAcquire())
+        return;
 
-    if (s_loadedCiphersAndCerts)
+    const QMutexLocker locker(&initMutex);
+
+    if (initializationStarted || initialized.loadAcquire())
         return;
-    s_loadedCiphersAndCerts = true;
+
+    // Indicate that the initialization has already started in the current
+    // thread in case of recursive calls. The atomic variable cannot be used
+    // for this because it is checked without holding the init mutex.
+    initializationStarted = true;
+
+    auto guard = qScopeGuard([] { initialized.storeRelease(1); });
 
     resetDefaultCiphers();
     resetDefaultEllipticCurves();
diff --git a/src/plugins/tls/openssl/qtlsbackend_openssl_p.h b/src/plugins/tls/openssl/qtlsbackend_openssl_p.h
index 6ff1052957..b9f1f95df0 100644
--- a/src/plugins/tls/openssl/qtlsbackend_openssl_p.h
+++ b/src/plugins/tls/openssl/qtlsbackend_openssl_p.h
@@ -42,7 +42,6 @@ public:
     static void clearErrorQueue();
 
     // Index used in SSL_get_ex_data to get the matching TlsCryptographerOpenSSL:
-    static bool s_loadedCiphersAndCerts;
     static int s_indexForSSLExtraData;
 
     static QString msgErrorsDuringHandshake();