1 files changed, 180 insertions, 0 deletions
diff --git a/Kernel/Locking/Spinlock.h b/Kernel/Locking/Spinlock.h
new file mode 100644
index 0000000000..b9e266e2ab
--- /dev/null
+++ b/Kernel/Locking/Spinlock.h
@@ -0,0 +1,180 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Atomic.h>
+#include <AK/Types.h>
+#include <Kernel/Arch/x86/Processor.h>
+#include <Kernel/Forward.h>
+
+namespace Kernel {
+
+template<typename BaseType = u32>
+class Spinlock {
+    AK_MAKE_NONCOPYABLE(Spinlock);
+    AK_MAKE_NONMOVABLE(Spinlock);
+
+public:
+    Spinlock() = default;
+
+    ALWAYS_INLINE u32 lock()
+    {
+        u32 prev_flags = cpu_flags();
+        Processor::enter_critical();
+        cli();
+        while (m_lock.exchange(1, AK::memory_order_acquire) != 0) {
+            Processor::wait_check();
+        }
+        return prev_flags;
+    }
+
+    ALWAYS_INLINE void unlock(u32 prev_flags)
+    {
+        VERIFY(is_locked());
+        m_lock.store(0, AK::memory_order_release);
+        if (prev_flags & 0x200)
+            sti();
+        else
+            cli();
+        Processor::leave_critical();
+    }
+
+    [[nodiscard]] ALWAYS_INLINE bool is_locked() const
+    {
+        return m_lock.load(AK::memory_order_relaxed) != 0;
+    }
+
+    ALWAYS_INLINE void initialize()
+    {
+        m_lock.store(0, AK::memory_order_relaxed);
+    }
+
+private:
+    Atomic<BaseType> m_lock { 0 };
+};
+
+class RecursiveSpinlock {
+    AK_MAKE_NONCOPYABLE(RecursiveSpinlock);
+    AK_MAKE_NONMOVABLE(RecursiveSpinlock);
+
+public:
+    RecursiveSpinlock() = default;
+
+    ALWAYS_INLINE u32 lock()
+    {
+        u32 prev_flags = cpu_flags();
+        cli();
+        Processor::enter_critical();
+        auto& proc = Processor::current();
+        FlatPtr cpu = FlatPtr(&proc);
+        FlatPtr expected = 0;
+        while (!m_lock.compare_exchange_strong(expected, cpu, AK::memory_order_acq_rel)) {
+            if (expected == cpu)
+                break;
+            Processor::wait_check();
+            expected = 0;
+        }
+        m_recursions++;
+        return prev_flags;
+    }
+
+    ALWAYS_INLINE void unlock(u32 prev_flags)
+    {
+        VERIFY(m_recursions > 0);
+        VERIFY(m_lock.load(AK::memory_order_relaxed) == FlatPtr(&Processor::current()));
+        if (--m_recursions == 0)
+            m_lock.store(0, AK::memory_order_release);
+        if (prev_flags & 0x200)
+            sti();
+        else
+            cli();
+        Processor::leave_critical();
+    }
+
+    [[nodiscard]] ALWAYS_INLINE bool is_locked() const
+    {
+        return m_lock.load(AK::memory_order_relaxed) != 0;
+    }
+
+    [[nodiscard]] ALWAYS_INLINE bool own_lock() const
+    {
+        return m_lock.load(AK::memory_order_relaxed) == FlatPtr(&Processor::current());
+    }
+
+    ALWAYS_INLINE void initialize()
+    {
+        m_lock.store(0, AK::memory_order_relaxed);
+    }
+
+private:
+    Atomic<FlatPtr> m_lock { 0 };
+    u32 m_recursions { 0 };
+};
+
+template<typename LockType>
+class [[nodiscard]] ScopedSpinlock {
+
+    AK_MAKE_NONCOPYABLE(ScopedSpinlock);
+
+public:
+    ScopedSpinlock() = delete;
+    ScopedSpinlock& operator=(ScopedSpinlock&&) = delete;
+
+    ScopedSpinlock(LockType& lock)
+        : m_lock(&lock)
+    {
+        VERIFY(m_lock);
+        m_prev_flags = m_lock->lock();
+        m_have_lock = true;
+    }
+
+    ScopedSpinlock(ScopedSpinlock&& from)
+        : m_lock(from.m_lock)
+        , m_prev_flags(from.m_prev_flags)
+        , m_have_lock(from.m_have_lock)
+    {
+        from.m_lock = nullptr;
+        from.m_prev_flags = 0;
+        from.m_have_lock = false;
+    }
+
+    ~ScopedSpinlock()
+    {
+        if (m_lock && m_have_lock) {
+            m_lock->unlock(m_prev_flags);
+        }
+    }
+
+    ALWAYS_INLINE void lock()
+    {
+        VERIFY(m_lock);
+        VERIFY(!m_have_lock);
+        m_prev_flags = m_lock->lock();
+        m_have_lock = true;
+    }
+
+    ALWAYS_INLINE void unlock()
+    {
+        VERIFY(m_lock);
+        VERIFY(m_have_lock);
+        m_lock->unlock(m_prev_flags);
+        m_prev_flags = 0;
+        m_have_lock = false;
+    }
+
+    [[nodiscard]] ALWAYS_INLINE bool have_lock() const
+    {
+        return m_have_lock;
+    }
+
+private:
+    LockType* m_lock { nullptr };
+    u32 m_prev_flags { 0 };
+    bool m_have_lock { false };
+};
+
+}