Prevent interface lockups during startup with multiple tabs

Fixes #11998

Avoids UI lockups by removing several unnecessary mutex blocks  and avoiding redundant key detection calls.

Author: droidmonkey

src/keys/drivers/YubiKey.cpp

@@ -73,31 +73,29 @@ bool YubiKey::isInitialized()
 
 bool YubiKey::findValidKeys()
 {
+    // Block operations on hardware keys while scanning
     QMutexLocker lock(&s_interfaceMutex);
 
-    findValidKeys(lock);
-
-    return !m_usbKeys.isEmpty() || !m_pcscKeys.isEmpty();
-}
-
-void YubiKey::findValidKeys(const QMutexLocker& locker)
-{
-    // Check QMutexLocker since version 6.4
-    Q_UNUSED(locker);
-
     m_connectedKeys = 0;
+    m_findingKeys = true;
     m_usbKeys = YubiKeyInterfaceUSB::instance()->findValidKeys(m_connectedKeys);
     m_pcscKeys = YubiKeyInterfacePCSC::instance()->findValidKeys(m_connectedKeys);
+    m_findingKeys = false;
+
+    return !m_usbKeys.isEmpty() || !m_pcscKeys.isEmpty();
 }
 
 void YubiKey::findValidKeysAsync()
 {
-    QtConcurrent::run([this] { emit detectComplete(findValidKeys()); });
+    // Don't start another scan if we are already doing one
+    if (!m_findingKeys) {
+        m_findingKeys = true;
+        QtConcurrent::run([this] { emit detectComplete(findValidKeys()); });
+    }
 }
 
 YubiKey::KeyMap YubiKey::foundKeys()
 {
-    QMutexLocker lock(&s_interfaceMutex);
     KeyMap foundKeys = m_usbKeys;
     foundKeys.unite(m_pcscKeys);
 
@@ -106,15 +104,11 @@ YubiKey::KeyMap YubiKey::foundKeys()
 
 int YubiKey::connectedKeys()
 {
-    QMutexLocker lock(&s_interfaceMutex);
-
     return m_connectedKeys;
 }
 
 QString YubiKey::errorMessage()
 {
-    QMutexLocker lock(&s_interfaceMutex);
-
     QString error;
     error.clear();
     if (!m_error.isNull()) {
@@ -176,14 +170,8 @@ YubiKey::ChallengeResult
 YubiKey::challenge(YubiKeySlot slot, const QByteArray& challenge, Botan::secure_vector<char>& response)
 {
     QMutexLocker lock(&s_interfaceMutex);
-
     m_error.clear();
 
-    // Make sure we tried to find available keys
-    if (m_usbKeys.isEmpty() && m_pcscKeys.isEmpty()) {
-        findValidKeys(lock);
-    }
-
     if (m_usbKeys.contains(slot)) {
         return YubiKeyInterfaceUSB::instance()->challenge(slot, challenge, response);
     }

src/keys/drivers/YubiKey.h

@@ -84,14 +84,14 @@ class YubiKey : public QObject
 private:
     explicit YubiKey();
 
-    void findValidKeys(const QMutexLocker& locker);
-
     static YubiKey* m_instance;
 
     QTimer m_interactionTimer;
     bool m_initialized = false;
+    bool m_findingKeys = false;
     QString m_error;
 
+    // Prevents multiple simultaneous operations on hardware keys
     static QMutex s_interfaceMutex;
 
     KeyMap m_usbKeys;