Kernel: Execute timer handlers outside of irq handler

This allows us to do things in timer handlers that involve e.g. scheduling,
such as using the Lock class or unblocking threads.

Kernel/TimerQueue.cpp

@@ -272,19 +272,24 @@ void TimerQueue::fire()
 
  while (timer && timer->now() > timer->m_expires) {
  queue.list.remove(timer);
+ timer->set_queued(false);
+
  m_timers_executing.append(timer);
 
  update_next_timer_due(queue);
 
  lock.unlock();
- timer->m_callback();
- lock.lock();
 
- m_timers_executing.remove(timer);
- timer->set_queued(false);
- // Drop the reference we added when queueing the timer
- timer->unref();
+ // Defer executing the timer outside of the irq handler
+ Processor::current().deferred_call_queue([this, timer]() {
+ timer->m_callback();
+ ScopedSpinLock lock(g_timerqueue_lock);
+ m_timers_executing.remove(timer);
+ // Drop the reference we added when queueing the timer
+ timer->unref();
+ });
 
+ lock.lock();
  timer = queue.list.head();
  }
  };