Kernel: Rewrite ThreadBlocker

This gets rid of a very old bug where kernel panics when thread is being
woken up and unblocked at the same time on different cores. This
required adding a new lock to SchedulerQueue::Node and adding a cap to
how many threads a threadblocker can simultaneously block. I don't think
I ever block more than five threads on the same ThreadBlocker so this
should be fine.

kernel/include/kernel/Scheduler.h

@@ -14,33 +14,12 @@ namespace Kernel
 	class BaseMutex;
 	class Thread;
 	class ThreadBlocker;
+	struct SchedulerQueueNode;
 
 	class SchedulerQueue
 	{
 	public:
-		struct Node
-		{
-			Node(Thread* thread)
-				: thread(thread)
-			{}
-
-			Thread* const thread;
-
-			Node* next { nullptr };
-			Node* prev { nullptr };
-
-			uint64_t wake_time_ns { static_cast<uint64_t>(-1) };
-
-			ThreadBlocker* blocker { nullptr };
-			Node* block_chain_next { nullptr };
-			Node* block_chain_prev { nullptr };
-
-			ProcessorID processor_id { PROCESSOR_NONE };
-			bool blocked { false };
-
-			uint64_t last_start_ns { 0 };
-			uint64_t time_used_ns  { 0 };
-		};
+		using Node = SchedulerQueueNode;
 
 	public:
 		void add_thread_to_back(Node*);

kernel/include/kernel/SchedulerQueueNode.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <kernel/ProcessorID.h>
+#include <kernel/Lock/SpinLock.h>
+
+namespace Kernel
+{
+
+	class Thread;
+	class ThreadBlocker;
+
+	struct SchedulerQueueNode
+	{
+		SchedulerQueueNode(Thread* thread)
+			: thread(thread)
+		{}
+
+		Thread* const thread;
+
+		SchedulerQueueNode* next { nullptr };
+		SchedulerQueueNode* prev { nullptr };
+
+		uint64_t wake_time_ns { static_cast<uint64_t>(-1) };
+
+		SpinLock blocker_lock;
+		ThreadBlocker* blocker { nullptr };
+
+		ProcessorID processor_id { PROCESSOR_NONE };
+		bool blocked { false };
+
+		uint64_t last_start_ns { 0 };
+		uint64_t time_used_ns  { 0 };
+	};
+
+}

kernel/include/kernel/ThreadBlocker.h

@@ -33,7 +33,9 @@ namespace Kernel
 
 	private:
 		SpinLock m_lock;
-		SchedulerQueue::Node* m_block_chain { nullptr };
+
+		SchedulerQueue::Node* m_block_chain[32] {};
+		size_t m_block_chain_length { 0 };
 
 		friend class Scheduler;
 	};