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;
 	};

kernel/kernel/Scheduler.cpp

@@ -4,6 +4,7 @@
 #include <kernel/Lock/Mutex.h>
 #include <kernel/Process.h>
 #include <kernel/Scheduler.h>
+#include <kernel/SchedulerQueueNode.h>
 #include <kernel/Thread.h>
 #include <kernel/Timer/Timer.h>
 
@@ -307,8 +308,11 @@ namespace Kernel
 			while (!m_block_queue.empty() && current_ns >= m_block_queue.front()->wake_time_ns)
 			{
 				auto* node = m_block_queue.pop_front();
-				if (node->blocker)
-					node->blocker->remove_blocked_thread(node);
+				{
+					SpinLockGuard _(node->blocker_lock);
+					if (node->blocker)
+						node->blocker->remove_blocked_thread(node);
+				}
 				node->blocked = false;
 				update_most_loaded_node_queue(node, &m_run_queue);
 				m_run_queue.add_thread_to_back(node);
@@ -336,8 +340,11 @@ namespace Kernel
 				return;
 			if (node != m_current)
 				m_block_queue.remove_node(node);
-			if (node->blocker)
-				node->blocker->remove_blocked_thread(node);
+			{
+				SpinLockGuard _(node->blocker_lock);
+				if (node->blocker)
+					node->blocker->remove_blocked_thread(node);
+			}
 			node->blocked = false;
 			if (node != m_current)
 				m_run_queue.add_thread_to_back(node);
@@ -618,8 +625,13 @@ namespace Kernel
 
 		m_current->blocked = true;
 		m_current->wake_time_ns = wake_time_ns;
-		if (blocker)
-			blocker->add_thread_to_block_queue(m_current);
+
+		{
+			SpinLockGuard _(m_current->blocker_lock);
+			if (blocker)
+				blocker->add_thread_to_block_queue(m_current);
+		}
+
 		update_most_loaded_node_queue(m_current, &m_block_queue);
 
 		uint32_t lock_depth = 0;
@@ -642,10 +654,7 @@ namespace Kernel
 
 	void Scheduler::unblock_thread(Thread* thread)
 	{
-		auto state = Processor::get_interrupt_state();
-		Processor::set_interrupt_state(InterruptState::Disabled);
 		unblock_thread(thread->m_scheduler_node);
-		Processor::set_interrupt_state(state);
 	}
 
 	Thread& Scheduler::current_thread()

kernel/kernel/ThreadBlocker.cpp

@@ -1,4 +1,5 @@
 #include <kernel/Processor.h>
+#include <kernel/SchedulerQueueNode.h>
 #include <kernel/ThreadBlocker.h>
 #include <kernel/Timer/Timer.h>
 
@@ -22,71 +23,60 @@ namespace Kernel
 
 	void ThreadBlocker::unblock()
 	{
-		SchedulerQueue::Node* block_chain;
+		decltype(m_block_chain) temp_block_chain;
+		size_t temp_block_chain_length { 0 };
 
 		{
 			SpinLockGuard _(m_lock);
-			block_chain = m_block_chain;
-			m_block_chain = nullptr;
+			for (size_t i = 0; i < m_block_chain_length; i++)
+				temp_block_chain[i] = m_block_chain[i];
+			temp_block_chain_length = m_block_chain_length;
+			m_block_chain_length = 0;
 		}
 
-		for (auto* node = block_chain; node;)
-		{
-			ASSERT(node->blocked);
-
-			auto* next = node->block_chain_next;
-			node->blocker = nullptr;
-			node->block_chain_next = nullptr;
-			node->block_chain_prev = nullptr;
-			Processor::scheduler().unblock_thread(node);
-			node = next;
-		}
+		for (size_t i = 0; i < temp_block_chain_length; i++)
+			Processor::scheduler().unblock_thread(temp_block_chain[i]);
 	}
 
 	void ThreadBlocker::add_thread_to_block_queue(SchedulerQueue::Node* node)
 	{
+		ASSERT(node->blocker_lock.current_processor_has_lock());
+
+		SpinLockGuard _(m_lock);
+
+		ASSERT(m_block_chain_length < sizeof(m_block_chain) / sizeof(m_block_chain[0]));
+
 		ASSERT(node);
 		ASSERT(node->blocked);
 		ASSERT(node->blocker == nullptr);
-		ASSERT(node->block_chain_prev == nullptr);
-		ASSERT(node->block_chain_next == nullptr);
 
-		SpinLockGuard _(m_lock);
+		for (size_t i = 0 ; i < m_block_chain_length; i++)
+			ASSERT(m_block_chain[i] != node);
+		m_block_chain[m_block_chain_length++] = node;
+
 		node->blocker = this;
-		node->block_chain_prev = nullptr;
-		node->block_chain_next = m_block_chain;
-		if (m_block_chain)
-			m_block_chain->block_chain_prev = node;
-		m_block_chain = node;
 	}
 
 	void ThreadBlocker::remove_blocked_thread(SchedulerQueue::Node* node)
 	{
+		ASSERT(node->blocker_lock.current_processor_has_lock());
+
 		SpinLockGuard _(m_lock);
 
 		ASSERT(node);
 		ASSERT(node->blocked);
 		ASSERT(node->blocker == this);
 
-		if (node == m_block_chain)
+		for (size_t i = 0 ; i < m_block_chain_length; i++)
 		{
-			ASSERT(node->block_chain_prev == nullptr);
-			m_block_chain = node->block_chain_next;
-			if (m_block_chain)
-				m_block_chain->block_chain_prev = nullptr;
-		}
-		else
-		{
-			ASSERT(node->block_chain_prev);
-			node->block_chain_prev->block_chain_next = node->block_chain_next;
-			if (node->block_chain_next)
-				node->block_chain_next->block_chain_prev = node->block_chain_prev;
+			if (m_block_chain[i] != node)
+				continue;
+			for (size_t j = i + 1; j < m_block_chain_length; j++)
+				m_block_chain[j - 1] = m_block_chain[j];
+			m_block_chain_length--;
 		}
 
 		node->blocker = nullptr;
-		node->block_chain_next = nullptr;
-		node->block_chain_prev = nullptr;
 	}
 
-
 }