Index: head/sys/kern/kern_condvar.c
===================================================================
--- head/sys/kern/kern_condvar.c
+++ head/sys/kern/kern_condvar.c
@@ -122,7 +122,7 @@
 
 	sleepq_lock(cvp);
 
-	cvp->cv_waiters++;
+	atomic_add_int(&cvp->cv_waiters, 1);
 	if (lock == &Giant.lock_object)
 		mtx_assert(&Giant, MA_OWNED);
 	DROP_GIANT();
@@ -137,6 +137,7 @@
 			sleepq_lock(cvp);
 	}
 	sleepq_wait(cvp, 0);
+	atomic_subtract_int(&cvp->cv_waiters, 1);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -184,7 +185,7 @@
 
 	sleepq_lock(cvp);
 
-	cvp->cv_waiters++;
+	atomic_add_int(&cvp->cv_waiters, 1);
 	DROP_GIANT();
 
 	sleepq_add(cvp, lock, cvp->cv_description, SLEEPQ_CONDVAR, 0);
@@ -194,6 +195,7 @@
 	if (class->lc_flags & LC_SLEEPABLE)
 		sleepq_lock(cvp);
 	sleepq_wait(cvp, 0);
+	atomic_subtract_int(&cvp->cv_waiters, 1);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -240,7 +242,7 @@
 
 	sleepq_lock(cvp);
 
-	cvp->cv_waiters++;
+	atomic_add_int(&cvp->cv_waiters, 1);
 	if (lock == &Giant.lock_object)
 		mtx_assert(&Giant, MA_OWNED);
 	DROP_GIANT();
@@ -256,6 +258,7 @@
 			sleepq_lock(cvp);
 	}
 	rval = sleepq_wait_sig(cvp, 0);
+	atomic_subtract_int(&cvp->cv_waiters, 1);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -307,7 +310,7 @@
 
 	sleepq_lock(cvp);
 
-	cvp->cv_waiters++;
+	atomic_add_int(&cvp->cv_waiters, 1);
 	if (lock == &Giant.lock_object)
 		mtx_assert(&Giant, MA_OWNED);
 	DROP_GIANT();
@@ -323,6 +326,7 @@
 			sleepq_lock(cvp);
 	}
 	rval = sleepq_timedwait(cvp, 0);
+	atomic_subtract_int(&cvp->cv_waiters, 1);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -376,7 +380,7 @@
 
 	sleepq_lock(cvp);
 
-	cvp->cv_waiters++;
+	atomic_add_int(&cvp->cv_waiters, 1);
 	if (lock == &Giant.lock_object)
 		mtx_assert(&Giant, MA_OWNED);
 	DROP_GIANT();
@@ -393,6 +397,7 @@
 			sleepq_lock(cvp);
 	}
 	rval = sleepq_timedwait_sig(cvp, 0);
+	atomic_subtract_int(&cvp->cv_waiters, 1);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -421,10 +426,8 @@
 
 	wakeup_swapper = 0;
 	sleepq_lock(cvp);
-	if (cvp->cv_waiters > 0) {
-		cvp->cv_waiters--;
+	if (cvp->cv_waiters > 0)
 		wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0, 0);
-	}
 	sleepq_release(cvp);
 	if (wakeup_swapper)
 		kick_proc0();
@@ -447,10 +450,8 @@
 	if (pri == -1)
 		pri = 0;
 	sleepq_lock(cvp);
-	if (cvp->cv_waiters > 0) {
-		cvp->cv_waiters = 0;
+	if (cvp->cv_waiters > 0)
 		wakeup_swapper = sleepq_broadcast(cvp, SLEEPQ_CONDVAR, pri, 0);
-	}
 	sleepq_release(cvp);
 	if (wakeup_swapper)
 		kick_proc0();
Index: head/sys/sys/condvar.h
===================================================================
--- head/sys/sys/condvar.h
+++ head/sys/sys/condvar.h
@@ -45,7 +45,7 @@
  */
 struct cv {
 	const char	*cv_description;
-	int		cv_waiters;
+	volatile int	cv_waiters;
 };
 
 #ifdef _KERNEL