Kernel: Properly keep track of mutex lock data in the guest memory. This fixes userland locking/unlocking.

src/citra_qt/debugger/wait_tree.cpp

@@ -257,10 +257,9 @@ std::vector<std::unique_ptr<WaitTreeItem>> WaitTreeMutex::GetChildren() const {
     std::vector<std::unique_ptr<WaitTreeItem>> list(WaitTreeWaitObject::GetChildren());
 
     const auto& mutex = static_cast<const Kernel::Mutex&>(object);
-    if (mutex.lock_count) {
-        list.push_back(
-            std::make_unique<WaitTreeText>(tr("locked %1 times by thread:").arg(mutex.lock_count)));
-        list.push_back(std::make_unique<WaitTreeThread>(*mutex.holding_thread));
+    if (mutex.GetHasWaiters()) {
+        list.push_back(std::make_unique<WaitTreeText>(tr("locked by thread:")));
+        list.push_back(std::make_unique<WaitTreeThread>(*mutex.GetHoldingThread()));
     } else {
         list.push_back(std::make_unique<WaitTreeText>(tr("free")));
     }

src/core/hle/kernel/mutex.cpp

@@ -17,8 +17,8 @@ namespace Kernel {
 
 void ReleaseThreadMutexes(Thread* thread) {
     for (auto& mtx : thread->held_mutexes) {
-        mtx->lock_count = 0;
-        mtx->holding_thread = nullptr;
+        mtx->SetHasWaiters(false);
+        mtx->SetHoldingThread(nullptr);
         mtx->WakeupAllWaitingThreads();
     }
     thread->held_mutexes.clear();
@@ -31,10 +31,8 @@ SharedPtr<Mutex> Mutex::Create(SharedPtr<Kernel::Thread> holding_thread, VAddr g
                                std::string name) {
     SharedPtr<Mutex> mutex(new Mutex);
 
-    mutex->lock_count = 0;
     mutex->guest_addr = guest_addr;
     mutex->name = std::move(name);
-    mutex->holding_thread = nullptr;
 
     // If mutex was initialized with a holding thread, acquire it by the holding thread
     if (holding_thread) {
@@ -51,56 +49,32 @@ SharedPtr<Mutex> Mutex::Create(SharedPtr<Kernel::Thread> holding_thread, VAddr g
 }
 
 bool Mutex::ShouldWait(Thread* thread) const {
-    return lock_count > 0 && thread != holding_thread;
+    auto holding_thread = GetHoldingThread();
+    return holding_thread != nullptr && thread != holding_thread;
 }
 
 void Mutex::Acquire(Thread* thread) {
     ASSERT_MSG(!ShouldWait(thread), "object unavailable!");
 
-    // Actually "acquire" the mutex only if we don't already have it
-    if (lock_count == 0) {
     priority = thread->current_priority;
     thread->held_mutexes.insert(this);
-        holding_thread = thread;
+    SetHoldingThread(thread);
     thread->UpdatePriority();
-        UpdateGuestState();
     Core::System::GetInstance().PrepareReschedule();
 }
 
-    lock_count++;
-}
-
 ResultCode Mutex::Release(Thread* thread) {
+    auto holding_thread = GetHoldingThread();
+    ASSERT(holding_thread);
+
     // We can only release the mutex if it's held by the calling thread.
-    if (thread != holding_thread) {
-        if (holding_thread) {
-            LOG_ERROR(
-                Kernel,
-                "Tried to release a mutex (owned by thread id %u) from a different thread id %u",
-                holding_thread->thread_id, thread->thread_id);
-        }
-        // TODO(bunnei): Use correct error code
-        return ResultCode(-1);
-    }
+    ASSERT(thread == holding_thread);
 
-    // Note: It should not be possible for the situation where the mutex has a holding thread with a
-    // zero lock count to occur. The real kernel still checks for this, so we do too.
-    if (lock_count <= 0) {
-        // TODO(bunnei): Use correct error code
-        return ResultCode(-1);
-    }
-
-    lock_count--;
-
-    // Yield to the next thread only if we've fully released the mutex
-    if (lock_count == 0) {
     holding_thread->held_mutexes.erase(this);
     holding_thread->UpdatePriority();
-        holding_thread = nullptr;
+    SetHoldingThread(nullptr);
     WakeupAllWaitingThreads();
-        UpdateGuestState();
     Core::System::GetInstance().PrepareReschedule();
-    }
 
     return RESULT_SUCCESS;
 }
@@ -108,19 +82,20 @@ ResultCode Mutex::Release(Thread* thread) {
 void Mutex::AddWaitingThread(SharedPtr<Thread> thread) {
     WaitObject::AddWaitingThread(thread);
     thread->pending_mutexes.insert(this);
+    SetHasWaiters(true);
     UpdatePriority();
-    UpdateGuestState();
 }
 
 void Mutex::RemoveWaitingThread(Thread* thread) {
     WaitObject::RemoveWaitingThread(thread);
     thread->pending_mutexes.erase(this);
+    if (!GetHasWaiters())
+        SetHasWaiters(!GetWaitingThreads().empty());
     UpdatePriority();
-    UpdateGuestState();
 }
 
 void Mutex::UpdatePriority() {
-    if (!holding_thread)
+    if (!GetHoldingThread())
         return;
 
     u32 best_priority = THREADPRIO_LOWEST;
@@ -131,21 +106,35 @@ void Mutex::UpdatePriority() {
 
     if (best_priority != priority) {
         priority = best_priority;
-        holding_thread->UpdatePriority();
+        GetHoldingThread()->UpdatePriority();
     }
 }
 
-void Mutex::UpdateGuestState() {
+Handle Mutex::GetOwnerHandle() const {
     GuestState guest_state{Memory::Read32(guest_addr)};
-    guest_state.has_waiters.Assign(!GetWaitingThreads().empty());
-    guest_state.holding_thread_handle.Assign(holding_thread ? holding_thread->guest_handle : 0);
+    return guest_state.holding_thread_handle;
+}
+
+SharedPtr<Thread> Mutex::GetHoldingThread() const {
+    GuestState guest_state{Memory::Read32(guest_addr)};
+    return g_handle_table.Get<Thread>(guest_state.holding_thread_handle);
+}
+
+void Mutex::SetHoldingThread(SharedPtr<Thread> thread) {
+    GuestState guest_state{Memory::Read32(guest_addr)};
+    guest_state.holding_thread_handle.Assign(thread ? thread->guest_handle : 0);
     Memory::Write32(guest_addr, guest_state.raw);
 }
 
-void Mutex::VerifyGuestState() {
+bool Mutex::GetHasWaiters() const {
     GuestState guest_state{Memory::Read32(guest_addr)};
-    ASSERT(guest_state.has_waiters == !GetWaitingThreads().empty());
-    ASSERT(guest_state.holding_thread_handle == holding_thread->guest_handle);
+    return guest_state.has_waiters != 0;
+}
+
+void Mutex::SetHasWaiters(bool has_waiters) {
+    GuestState guest_state{Memory::Read32(guest_addr)};
+    guest_state.has_waiters.Assign(has_waiters ? 1 : 0);
+    Memory::Write32(guest_addr, guest_state.raw);
 }
 
 } // namespace Kernel

src/core/hle/kernel/mutex.h

@@ -41,10 +41,8 @@ public:
         return HANDLE_TYPE;
     }
 
-    int lock_count;                   ///< Number of times the mutex has been acquired
     u32 priority;                     ///< The priority of the mutex, used for priority inheritance.
     std::string name;                 ///< Name of mutex (optional)
-    SharedPtr<Thread> holding_thread; ///< Thread that has acquired the mutex
     VAddr guest_addr;                 ///< Address of the guest mutex value
 
     /**
@@ -66,6 +64,19 @@ public:
      */
     ResultCode Release(Thread* thread);
 
+    /// Gets the handle to the holding process stored in the guest state.
+    Handle GetOwnerHandle() const;
+
+    /// Gets the Thread pointed to by the owner handle
+    SharedPtr<Thread> GetHoldingThread() const;
+    /// Sets the holding process handle in the guest state.
+    void SetHoldingThread(SharedPtr<Thread> thread);
+
+    /// Returns the has_waiters bit in the guest state.
+    bool GetHasWaiters() const;
+    /// Sets the has_waiters bit in the guest state.
+    void SetHasWaiters(bool has_waiters);
+
 private:
     Mutex();
     ~Mutex() override;
@@ -79,12 +90,6 @@ private:
         BitField<30, 1, u32_le> has_waiters;
     };
     static_assert(sizeof(GuestState) == 4, "GuestState size is incorrect");
-
-    /// Updates the state of the object tracking this mutex in guest memory
-    void UpdateGuestState();
-
-    /// Verifies the state of the object tracking this mutex in guest memory
-    void VerifyGuestState();
 };
 
 /**

src/core/hle/kernel/svc.cpp

@@ -204,7 +204,6 @@ static ResultCode LockMutex(Handle holding_thread_handle, VAddr mutex_addr,
     SharedPtr<Thread> holding_thread = g_handle_table.Get<Thread>(holding_thread_handle);
     SharedPtr<Thread> requesting_thread = g_handle_table.Get<Thread>(requesting_thread_handle);
 
-    ASSERT(holding_thread);
     ASSERT(requesting_thread);
 
     SharedPtr<Mutex> mutex = g_object_address_table.Get<Mutex>(mutex_addr);
@@ -214,6 +213,8 @@ static ResultCode LockMutex(Handle holding_thread_handle, VAddr mutex_addr,
         mutex->name = Common::StringFromFormat("mutex-%llx", mutex_addr);
     }
 
+    ASSERT(holding_thread == mutex->GetHoldingThread());
+
     return WaitSynchronization1(mutex, requesting_thread.get());
 }
 
@@ -491,6 +492,8 @@ static ResultCode WaitProcessWideKeyAtomic(VAddr mutex_addr, VAddr semaphore_add
         mutex->name = Common::StringFromFormat("mutex-%llx", mutex_addr);
     }
 
+    ASSERT(mutex->GetOwnerHandle() == thread_handle);
+
     SharedPtr<Semaphore> semaphore = g_object_address_table.Get<Semaphore>(semaphore_addr);
     if (!semaphore) {
         // Create a new semaphore for the specified address if one does not already exist