Kernel: Make Locker remember whether the lock is held

This allows temporarily unlocking a lock or re-locking it, and it will
only unlock if it is still being held.

Fixes SerenityOS#4352

Kernel/Lock.h

@@ -110,12 +110,27 @@ class Locker {
  {
  m_lock.lock(mode);
  }
- ALWAYS_INLINE ~Locker() { unlock(); }
- ALWAYS_INLINE void unlock() { m_lock.unlock(); }
- ALWAYS_INLINE void lock(Lock::Mode mode = Lock::Mode::Exclusive) { m_lock.lock(mode); }
+ ALWAYS_INLINE ~Locker()
+ {
+ if (m_locked)
+ unlock();
+ }
+ ALWAYS_INLINE void unlock()
+ {
+ ASSERT(m_locked);
+ m_locked = false;
+ m_lock.unlock();
+ }
+ ALWAYS_INLINE void lock(Lock::Mode mode = Lock::Mode::Exclusive)
+ {
+ ASSERT(!m_locked);
+ m_locked = true;
+ m_lock.lock(mode);
+ }
 
 private:
  Lock& m_lock;
+ bool m_locked { true };
 };
 
 #ifdef LOCK_DEBUG