Kernel: Fix Lock racing to the WaitQueue

There was a time window between releasing Lock::m_lock and calling into
the lock's WaitQueue where someone else could take m_lock and bring two
threads into a deadlock situation.

Fix this issue by holding Lock::m_lock until interrupts are disabled by
either Thread::wait_on() or WaitQueue::wake_one().

1 files changed, 2 insertions, 1 deletions

diff --git a/Kernel/Thread.h b/Kernel/Thread.h
index c17b43bbba..18f8546464 100644
--- a/Kernel/Thread.h
+++ b/Kernel/Thread.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <AK/Atomic.h>
 #include <AK/Function.h>
 #include <AK/IntrusiveList.h>
 #include <AK/OwnPtr.h>
@@ -300,7 +301,7 @@ public:
         return block<ConditionBlocker>(state_string, move(condition));
     }
 
-    void wait_on(WaitQueue& queue, Thread* beneficiary = nullptr, const char* reason = nullptr);
+    void wait_on(WaitQueue& queue, Atomic<bool>* lock = nullptr, Thread* beneficiary = nullptr, const char* reason = nullptr);
     void wake_from_queue();
 
     void unblock();