Kernel: Enhance WaitQueue to remember pending wakes

If WaitQueue::wake_all, WaitQueue::wake_one, or WaitQueue::wake_n
is called but nobody is currently waiting, we should remember that
fact and prevent someone from waiting after such a request. This
solves a race condition where the Finalizer thread is notified
to finalize a thread, but it is not (yet) waiting on this queue.

Fixes #2693

1 files changed, 7 insertions, 1 deletions

diff --git a/Kernel/Thread.cpp b/Kernel/Thread.cpp
index bf0dcaac4e..8f21bef644 100644
--- a/Kernel/Thread.cpp
+++ b/Kernel/Thread.cpp
@@ -872,12 +872,18 @@ 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);
+            if (!queue.enqueue(*Thread::current())) {
+                // The WaitQueue was already requested to wake someone when
+                // nobody was waiting. So return right away as we shouldn't
+                // be waiting
+                return BlockResult::NotBlocked;
+            }
+
             did_unlock = unlock_process_if_locked();
             if (lock)
                 *lock = false;
             set_state(State::Queued);
             m_wait_reason = reason;
-            queue.enqueue(*Thread::current());
 
     
             if (timeout) {