Kernel: Allow killing queued threads

We need to dequeue and wake threads that are waiting if the process
terminates.

Fixes #3603 without the HackStudio fixes in #3606.

Kernel/Thread.cpp

@@ -151,6 +151,14 @@ void Thread::set_should_die()
             // the kernel stacks can clean up. We won't ever return back
             // to user mode, though
             resume_from_stopped();
+        } else if (state() == Queued) {
+            // m_queue can only be accessed safely if g_scheduler_lock is held!
+            if (m_queue) {
+                m_queue->dequeue(*this);
+                m_queue = nullptr;
+                // Wake the thread
+                wake_from_queue();
+            }
         }
     }
 
@@ -973,6 +981,8 @@ Thread::BlockResult Thread::wait_on(WaitQueue& queue, const char* reason, timeva
         // we need to wait until the scheduler lock is released again
         {
             ScopedSpinLock sched_lock(g_scheduler_lock);
+            // m_queue can only be accessed safely if g_scheduler_lock is held!
+            m_queue = &queue;
             if (!queue.enqueue(*current_thread)) {
                 // The WaitQueue was already requested to wake someone when
                 // nobody was waiting. So return right away as we shouldn't
@@ -1026,9 +1036,18 @@ Thread::BlockResult Thread::wait_on(WaitQueue& queue, const char* reason, timeva
         // scheduler lock, which is held when we insert into the queue
         ScopedSpinLock sched_lock(g_scheduler_lock);
 
-        // If our thread was still in the queue, we timed out
-        if (queue.dequeue(*current_thread))
-            result = BlockResult::InterruptedByTimeout;
+        if (m_queue) {
+            ASSERT(m_queue == &queue);
+            // If our thread was still in the queue, we timed out
+            m_queue = nullptr;
+            if (queue.dequeue(*current_thread))
+                result = BlockResult::InterruptedByTimeout;
+        } else {
+            // Our thread was already removed from the queue. The only
+            // way this can happen if someone else is trying to kill us.
+            // In this case, the queue should not contain us anymore.
+            return BlockResult::InterruptedByDeath;
+        }
 
         // Make sure we cancel the timer if woke normally.
         if (timeout && !result.was_interrupted())

Kernel/Thread.h

@@ -438,12 +438,12 @@ public:
         // to clean up now while we're still holding m_lock
         t.was_unblocked();
 
-        if (t.was_interrupted_by_signal())
-            return BlockResult::InterruptedBySignal;
-
         if (t.was_interrupted_by_death())
             return BlockResult::InterruptedByDeath;
 
+        if (t.was_interrupted_by_signal())
+            return BlockResult::InterruptedBySignal;
+
         return BlockResult::WokeNormally;
     }
 
@@ -634,6 +634,7 @@ private:
     Blocker* m_blocker { nullptr };
     timespec* m_blocker_timeout { nullptr };
     const char* m_wait_reason { nullptr };
+    WaitQueue* m_queue { nullptr };
 
     Atomic<bool> m_is_active { false };
     bool m_is_joinable { true };