Kernel: Make PIT counter atomic with spinlock

kernel/include/kernel/Timer/PIT.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <kernel/Interruptable.h>
+#include <kernel/Lock/SpinLock.h>
 #include <kernel/Timer/Timer.h>
 
 namespace Kernel
@@ -19,9 +20,11 @@ namespace Kernel
 
 	private:
 		void initialize();
+		uint64_t read_counter() const;
 
 	private:
-		volatile uint64_t m_system_time { 0 };
+		mutable SpinLock m_lock;
+		uint64_t m_system_time { 0 };
 	};
 
 }

kernel/kernel/Timer/PIT.cpp

@@ -54,23 +54,32 @@ namespace Kernel
 
 	void PIT::handle_irq()
 	{
-		m_system_time = m_system_time + 1;
+		{
+			SpinLockGuard _(m_lock);
+			m_system_time++;
+		}
 		Kernel::Scheduler::get().timer_reschedule();
 	}
 
+	uint64_t PIT::read_counter() const
+	{
+		SpinLockGuard _(m_lock);
+		return m_system_time;
+	}
+
 	uint64_t PIT::ms_since_boot() const
 	{
-		return m_system_time * (MS_PER_S / TICKS_PER_SECOND);
+		return read_counter() * (MS_PER_S / TICKS_PER_SECOND);
 	}
 
 	uint64_t PIT::ns_since_boot() const
 	{
-		return m_system_time * (NS_PER_S / TICKS_PER_SECOND);
+		return read_counter() * (NS_PER_S / TICKS_PER_SECOND);
 	}
 
 	timespec PIT::time_since_boot() const
 	{
-		uint64_t ticks = m_system_time;
+		uint64_t ticks = read_counter();
 		return timespec {
 			.tv_sec = ticks / TICKS_PER_SECOND,
 			.tv_nsec = (long)((ticks % TICKS_PER_SECOND) * (NS_PER_S / TICKS_PER_SECOND))