lock-free check leads to a race condition

db4dc1c3 · Nickolai Zeldovich · 85b77136 · db4dc1c3
--- a/condvar.c
+++ b/condvar.c
@@ -52,8 +52,9 @@ cv_sleep(struct condvar *cv, struct spinlock *lk)
 void
 cv_wakeup(struct condvar *cv)
 {
-  if (!cv->waiters)
+  // XXX race with cv_sleep()
-    return;
+  // if (!cv->waiters)
+  //   return;
  acquire(&cv->lock);
  while(cv->waiters) {