Kernel: Make TTY write lock a spinlock

I don't really like this but its needed with the current architecture to
allow printing while interrupts are disabled. I was hitting a dead lock
on few real machines

kernel/include/kernel/Terminal/TTY.h

@@ -100,9 +100,9 @@ namespace Kernel
 		termios m_termios;
 
 	protected:
-		Mutex m_mutex;
+		Mutex m_input_mutex;
 
-		Mutex m_write_lock;
+		RecursiveSpinLock m_write_lock;
 		ThreadBlocker m_write_blocker;
 	};
 

kernel/include/kernel/Terminal/VirtualTTY.h

@@ -21,6 +21,8 @@ namespace Kernel
 
 		void clear() override;
 
+		BAN::ErrorOr<void> set_terminal_driver(BAN::RefPtr<TerminalDriver>);
+
 	protected:
 		BAN::StringView name() const override { return m_name; }
 		bool putchar_impl(uint8_t ch) override;

kernel/kernel/Terminal/PseudoTerminal.cpp

@@ -146,7 +146,7 @@ namespace Kernel
 		auto slave = m_slave.lock();
 		if (!slave)
 			return BAN::Error::from_errno(EIO);
-		LockGuard _(slave->m_mutex);
+		LockGuard _(slave->m_input_mutex);
 		for (size_t i = 0; i < buffer.size(); i++)
 			slave->handle_input_byte(buffer[i]);
 		return buffer.size();

kernel/kernel/Terminal/TTY.cpp

@@ -6,6 +6,7 @@
 #include <kernel/FS/DevFS/FileSystem.h>
 #include <kernel/FS/VirtualFileSystem.h>
 #include <kernel/Input/InputDevice.h>
+#include <kernel/Lock/BlockableSpinLock.h>
 #include <kernel/Lock/LockGuard.h>
 #include <kernel/Process.h>
 #include <kernel/Terminal/TTY.h>
@@ -220,7 +221,7 @@ namespace Kernel
 		if (ansi_c_str == nullptr)
 			return;
 
-		LockGuard _(m_mutex);
+		LockGuard _(m_input_mutex);
 		while (*ansi_c_str)
 			handle_input_byte(*ansi_c_str++);
 		after_write();
@@ -269,7 +270,7 @@ namespace Kernel
 		bool should_flush = false;
 		bool force_echo = false;
 
-		LockGuard _(m_mutex);
+		LockGuard _(m_input_mutex);
 
 		if (!(termios.c_lflag & ICANON))
 			should_flush = true;
@@ -377,7 +378,8 @@ namespace Kernel
 
 		const auto termios = get_termios();
 
-		LockGuard _(m_write_lock);
+		SpinLockGuard _(m_write_lock);
+
 		if (termios.c_oflag & OPOST)
 		{
 			if ((termios.c_oflag & ONLCR) && ch == NL)
@@ -385,14 +387,16 @@ namespace Kernel
 			if ((termios.c_oflag & OCRNL) && ch == CR)
 				return putchar_impl(NL);
 		}
+
 		return putchar_impl(ch);
 	}
 
 	BAN::ErrorOr<size_t> TTY::read_impl(off_t, BAN::ByteSpan buffer)
 	{
-		LockGuard _(m_mutex);
+		LockGuard _(m_input_mutex);
+
 		while (!m_output.flush)
-			TRY(Thread::current().block_or_eintr_indefinite(m_output.thread_blocker, &m_mutex));
+			TRY(Thread::current().block_or_eintr_indefinite(m_output.thread_blocker, &m_input_mutex));
 
 		if (m_output.buffer->empty())
 		{
@@ -424,13 +428,14 @@ namespace Kernel
 
 	BAN::ErrorOr<size_t> TTY::write_impl(off_t, BAN::ConstByteSpan buffer)
 	{
-		LockGuard write_guard(m_write_lock);
+		SpinLockGuard _(m_write_lock);
 
 		while (!can_write())
 		{
 			if (master_has_closed())
 				return BAN::Error::from_errno(EIO);
-			TRY(Thread::current().block_or_eintr_indefinite(m_write_blocker, &m_write_lock));
+			BlockableSpinLock block(m_write_lock);
+			TRY(Thread::current().block_or_eintr_indefinite(m_write_blocker, &block));
 		}
 
 		size_t written = 0;
@@ -447,15 +452,12 @@ namespace Kernel
 
 	void TTY::putchar_current(uint8_t ch)
 	{
-		ASSERT(s_tty);
+		auto tty = s_tty;
+		ASSERT(tty);
 
-		while (!s_tty->m_write_lock.try_lock())
+		SpinLockGuard _(tty->m_write_lock);
-			Processor::pause();
+		tty->putchar(ch);
-
+		tty->after_write();
-		s_tty->putchar(ch);
-		s_tty->after_write();
-
-		s_tty->m_write_lock.unlock();
 	}
 
 	bool TTY::is_initialized()

kernel/kernel/Terminal/VirtualTTY.cpp

@@ -50,17 +50,48 @@ namespace Kernel
 		, m_foreground(driver->palette()[15])
 		, m_background(driver->palette()[0])
 	{
-		m_width = m_terminal_driver->width();
+		MUST(set_terminal_driver(driver));
-		m_height = m_terminal_driver->height();
+	}
-		update_winsize(m_width, m_height);
 
-		m_buffer = new Cell[m_width * m_height];
+	BAN::ErrorOr<void> VirtualTTY::set_terminal_driver(BAN::RefPtr<TerminalDriver> terminal_driver)
-		ASSERT(m_buffer);
+	{
+		const uint32_t new_width = terminal_driver->width();
+		const uint32_t new_height = terminal_driver->height();
+
+		SpinLockGuard _(m_write_lock);
+
+		if (m_width != new_width || m_height != new_height)
+		{
+			Cell* new_buffer = new Cell[new_width * new_height];
+			ASSERT(new_buffer);
+
+			for (uint32_t i = 0; i < new_width * m_height; i++)
+				new_buffer[i] = { .foreground = m_foreground, .background = m_background, .codepoint = ' ' };
+
+			for (uint32_t y = 0; y < BAN::Math::min<uint32_t>(m_height, new_height); y++)
+				for (uint32_t x = 0; x < BAN::Math::min<uint32_t>(m_width, new_width); x++)
+					new_buffer[y * new_width + x] = m_buffer[y * m_width + x];
+
+			delete[] m_buffer;
+			m_buffer = new_buffer;
+			m_width = new_width;
+			m_height = new_height;
+		}
+
+		m_terminal_driver = terminal_driver;
+
+		for (uint32_t y = 0; y < m_height; y++)
+			for (uint32_t x = 0; x < m_width; x++)
+				render_from_buffer(x, y);
+
+		update_winsize(new_width, new_height);
+
+		return {};
 	}
 
 	void VirtualTTY::clear()
 	{
-		LockGuard _(m_write_lock);
+		SpinLockGuard _(m_write_lock);
 		for (uint32_t i = 0; i < m_width * m_height; i++)
 			m_buffer[i] = { .foreground = m_foreground, .background = m_background, .codepoint = ' ' };
 		m_terminal_driver->clear(m_background);
@@ -70,46 +101,14 @@ namespace Kernel
 	{
 		if (!m_terminal_driver->has_font())
 			return BAN::Error::from_errno(EINVAL);
-
+		TRY(m_terminal_driver->set_font(BAN::move(font)));
-		{
+		MUST(set_terminal_driver(m_terminal_driver));
-			LockGuard _(m_write_lock);
-
-			TRY(m_terminal_driver->set_font(BAN::move(font)));
-
-			uint32_t new_width = m_terminal_driver->width();
-			uint32_t new_height = m_terminal_driver->height();
-
-			if (m_width != new_width || m_height != new_height)
-			{
-				Cell* new_buffer = new Cell[new_width * new_height];
-				ASSERT(new_buffer);
-
-				for (uint32_t i = 0; i < new_width * m_height; i++)
-					new_buffer[i] = { .foreground = m_foreground, .background = m_background, .codepoint = ' ' };
-
-				for (uint32_t y = 0; y < BAN::Math::min<uint32_t>(m_height, new_height); y++)
-					for (uint32_t x = 0; x < BAN::Math::min<uint32_t>(m_width, new_width); x++)
-						new_buffer[y * new_width + x] = m_buffer[y * m_width + x];
-
-				delete[] m_buffer;
-				m_buffer = new_buffer;
-				m_width = new_width;
-				m_height = new_height;
-			}
-
-			for (uint32_t y = 0; y < m_height; y++)
-				for (uint32_t x = 0; x < m_width; x++)
-					render_from_buffer(x, y);
-		}
-
-		update_winsize(m_width, m_height);
-
 		return {};
 	}
 
 	void VirtualTTY::reset_ansi()
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 		m_ansi_state = {
 			.nums = { -1, -1, -1, -1, -1 },
 			.index = 0,
@@ -120,7 +119,7 @@ namespace Kernel
 
 	void VirtualTTY::handle_ansi_csi_color(uint8_t value)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 
 		auto& palette = m_terminal_driver->palette();
 
@@ -203,7 +202,8 @@ namespace Kernel
 
 	void VirtualTTY::handle_ansi_csi(uint8_t ch)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
+
 		switch (ch)
 		{
 			case '0' ... '9':
@@ -445,7 +445,7 @@ namespace Kernel
 
 	void VirtualTTY::render_from_buffer(uint32_t x, uint32_t y)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 		ASSERT(x < m_width && y < m_height);
 		const auto& cell = m_buffer[y * m_width + x];
 		m_terminal_driver->putchar_at(cell.codepoint, x, y, cell.foreground, cell.background);
@@ -453,7 +453,7 @@ namespace Kernel
 
 	void VirtualTTY::putchar_at(uint32_t codepoint, uint32_t x, uint32_t y)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 		ASSERT(x < m_width && y < m_height);
 		auto& cell = m_buffer[y * m_width + x];
 		cell.codepoint = codepoint;
@@ -464,6 +464,8 @@ namespace Kernel
 
 	void VirtualTTY::scroll_if_needed()
 	{
+		ASSERT(m_write_lock.current_processor_has_lock());
+
 		while (m_row >= m_height)
 		{
 			memmove(m_buffer, m_buffer + m_width, m_width * (m_height - 1) * sizeof(Cell));
@@ -487,7 +489,7 @@ namespace Kernel
 
 	void VirtualTTY::putcodepoint(uint32_t codepoint)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 
 		switch (codepoint)
 		{
@@ -533,7 +535,7 @@ namespace Kernel
 
 	bool VirtualTTY::putchar_impl(uint8_t ch)
 	{
-		ASSERT(m_write_lock.is_locked_by_current_thread());
+		ASSERT(m_write_lock.current_processor_has_lock());
 
 		uint32_t codepoint = ch;