NVFlinger: Lock race condition between CPU, Host Timing, VSync.

src/core/hle/service/nvflinger/nvflinger.cpp

@@ -36,10 +36,12 @@ NVFlinger::NVFlinger(Core::System& system) : system(system) {
     displays.emplace_back(2, "Edid", system);
     displays.emplace_back(3, "Internal", system);
     displays.emplace_back(4, "Null", system);
+    guard = std::make_shared<std::mutex>();
 
     // Schedule the screen composition events
     composition_event =
         Core::Timing::CreateEvent("ScreenComposition", [this](u64 userdata, s64 ns_late) {
+            Lock();
             Compose();
             const auto ticks = GetNextTicks();
             this->system.CoreTiming().ScheduleEvent(std::max<s64>(0LL, ticks - ns_late),

src/core/hle/service/nvflinger/nvflinger.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <memory>
+#include <mutex>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -79,6 +80,10 @@ public:
 
     s64 GetNextTicks() const;
 
+    std::unique_lock<std::mutex> Lock() {
+        return std::unique_lock{*guard};
+    }
+
 private:
     /// Finds the display identified by the specified ID.
     VI::Display* FindDisplay(u64 display_id);
@@ -108,6 +113,8 @@ private:
     /// Event that handles screen composition.
     std::shared_ptr<Core::Timing::EventType> composition_event;
 
+    std::shared_ptr<std::mutex> guard;
+
     Core::System& system;
 };