Kernel: Implement RecursivePrioritySpinLock

This locks won't allow locking from userspace thread if there is
kernel thread waiting to lock this.

kernel/kernel/SpinLock.cpp

@@ -80,4 +80,61 @@ namespace Kernel
 		return m_locker != -1;
 	}
 
+	void RecursivePrioritySpinLock::lock()
+	{
+		pid_t tid = Scheduler::current_tid();
+
+		bool has_priority = !Thread::current().is_userspace();
+
+		if (has_priority)
+		{
+			m_lock.lock();
+			m_queue_length++;
+			m_lock.unlock();
+		}
+
+		while (true)
+		{
+			m_lock.lock();
+			if (m_locker == tid)
+			{
+				m_lock_depth++;
+				break;
+			}
+			if (m_locker == -1 && (has_priority || m_queue_length == 0))
+			{
+				m_locker = tid;
+				m_lock_depth = 1;
+				break;
+			}
+			m_lock.unlock();
+		}
+
+		m_lock.unlock();
+	}
+
+	void RecursivePrioritySpinLock::unlock()
+	{
+		m_lock.lock();
+		
+		ASSERT(m_lock_depth > 0);
+		ASSERT(m_locker == Scheduler::current_tid());
+
+		bool has_priority = !Thread::current().is_userspace();
+		if (has_priority)
+			m_queue_length--;
+
+		m_lock_depth--;
+
+		if (m_lock_depth == 0)
+			m_locker = -1;
+		
+		m_lock.unlock();
+	}
+
+	bool RecursivePrioritySpinLock::is_locked() const
+	{
+		return m_locker != -1;
+	}
+
 }