Index: sys/sys/umtx.h
===================================================================
--- sys/sys/umtx.h	(revision 233082)
+++ sys/sys/umtx.h	(working copy)
@@ -55,7 +55,9 @@
 #define URWLOCK_READER_COUNT(c)	((c) & URWLOCK_MAX_READERS)
 
 /* _usem flags */
-#define SEM_NAMED	0x0002
+#define	SEM_NAMED	0x00000002
+#define	SEM_VER2	0x00000004
+#define	SEM_WAITERS	0x80000000
 
 /* op code for _umtx_op */
 #define	UMTX_OP_LOCK		0
Index: sys/kern/kern_umtx.c
===================================================================
--- sys/kern/kern_umtx.c	(revision 233082)
+++ sys/kern/kern_umtx.c	(working copy)
@@ -2870,18 +2870,39 @@
 	umtxq_insert(uq);
 	umtxq_unlock(&uq->uq_key);
 
-	casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
-	rmb();
-	count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
-	if (count != 0) {
-		umtxq_lock(&uq->uq_key);
-		umtxq_unbusy(&uq->uq_key);
-		umtxq_remove(uq);
-		umtxq_unlock(&uq->uq_key);
-		umtx_key_release(&uq->uq_key);
-		return (0);
+	if (__predict_false((flags & SEM_VER2) == 0)) {
+		casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
+		rmb();
+		count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
+		if (count != 0) {
+			umtxq_lock(&uq->uq_key);
+			umtxq_unbusy(&uq->uq_key);
+			umtxq_remove(uq);
+			umtxq_unlock(&uq->uq_key);
+			umtx_key_release(&uq->uq_key);
+			return (0);
+		}
+	} else {
+		count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
+		for (;;) {
+			if ((count & ~SEM_WAITERS) != 0) {
+				umtxq_lock(&uq->uq_key);
+				umtxq_unbusy(&uq->uq_key);
+				umtxq_remove(uq);
+				umtxq_unlock(&uq->uq_key);
+				umtx_key_release(&uq->uq_key);
+				return (0);
+			}
+			if ((count & SEM_WAITERS) == 0) {
+				int old = casuword32(__DEVOLATILE(uint32_t *,
+				  &sem->_count), count, count | SEM_WAITERS);
+				if (old == count)
+					break;
+				count = old;
+			} else
+				break;
+		}
 	}
-
 	umtxq_lock(&uq->uq_key);
 	umtxq_unbusy(&uq->uq_key);
 
@@ -2932,22 +2953,42 @@
 do_sem_wake(struct thread *td, struct _usem *sem)
 {
 	struct umtx_key key;
-	int error, cnt, nwake;
-	uint32_t flags;
+	int error, nwait;
+	uint32_t flags, count;
 
 	flags = fuword32(&sem->_flags);
 	if ((error = umtx_key_get(sem, TYPE_SEM, GET_SHARE(flags), &key)) != 0)
 		return (error);	
 	umtxq_lock(&key);
 	umtxq_busy(&key);
-	cnt = umtxq_count(&key);
-	nwake = umtxq_signal(&key, 1);
-	if (cnt <= nwake) {
-		umtxq_unlock(&key);
-		error = suword32(
-		    __DEVOLATILE(uint32_t *, &sem->_has_waiters), 0);
-		umtxq_lock(&key);
+	nwait = umtxq_count(&key);
+	umtxq_unlock(&key);
+	if ((flags & SEM_VER2) != 0) {
+		error = 0;
+		count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
+		for (;;) {
+			if (__predict_false((count & ~SEM_WAITERS) == __INT_MAX)) {
+				umtxq_lock(&key);
+				umtxq_unbusy(&key);
+				umtxq_unlock(&key);
+				return (ERANGE);
+			}
+			int newval = count + 1;
+			if (nwait <= 1)
+				newval &= ~SEM_WAITERS;
+			int old = casuword32(__DEVOLATILE(uint32_t *,
+			  &sem->_count), count, newval);
+			if (old == count)
+				break;
+			count = old;
+		}
+	} else {
+		if (nwait <= 1)
+			error = suword32(
+			    __DEVOLATILE(uint32_t *, &sem->_has_waiters), 0);
 	}
+	umtxq_lock(&key);
+	umtxq_signal(&key, 1);
 	umtxq_unbusy(&key);
 	umtxq_unlock(&key);
 	umtx_key_release(&key);
Index: lib/libc/gen/sem_new.c
===================================================================
--- lib/libc/gen/sem_new.c	(revision 233082)
+++ lib/libc/gen/sem_new.c	(working copy)
@@ -61,7 +61,8 @@
 __weak_reference(_sem_wait, sem_wait);
 
 #define SEM_PREFIX	"/tmp/SEMD"
-#define SEM_MAGIC	((u_int32_t)0x73656d31)
+#define SEM_MAGIC1	((u_int32_t)0x73656d31)
+#define SEM_MAGIC	((u_int32_t)0x73656d32)
 
 struct sem_nameinfo {
 	int open_count;
@@ -109,7 +110,7 @@
 sem_check_validity(sem_t *sem)
 {
 
-	if (sem->_magic == SEM_MAGIC)
+	if (sem->_magic == SEM_MAGIC || sem->_magic == SEM_MAGIC1)
 		return (0);
 	else {
 		errno = EINVAL;
@@ -130,7 +131,7 @@
 	sem->_magic = SEM_MAGIC;
 	sem->_kern._count = (u_int32_t)value;
 	sem->_kern._has_waiters = 0;
-	sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
+	sem->_kern._flags = (pshared ? USYNC_PROCESS_SHARED : 0) | SEM_VER2;
 	return (0);
 }
 
@@ -207,7 +208,7 @@
 		tmp._magic = SEM_MAGIC;
 		tmp._kern._has_waiters = 0;
 		tmp._kern._count = value;
-		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
+		tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED | SEM_VER2;
 		if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
 			flock(fd, LOCK_UN);
 			goto error;
@@ -325,20 +326,11 @@
 	if (sem_check_validity(sem) != 0)
 		return (-1);
 
-	*sval = (int)sem->_kern._count;
+	*sval = (int)sem->_kern._count & ~SEM_WAITERS;
 	return (0);
 }
 
 static __inline int
-usem_wake(struct _usem *sem)
-{
-	rmb();
-	if (!sem->_has_waiters)
-		return (0);
-	return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
-}
-
-static __inline int
 usem_wait(struct _usem *sem, const struct timespec *abstime)
 {
 	struct _umtx_time *tm_p, timeout;
@@ -358,19 +350,35 @@
 		    (void *)tm_size, __DECONST(void*, tm_p));
 }
 
+static inline int
+_trywait(sem_t *sem)
+{
+	int val;
+
+	if ((sem->_kern._flags & SEM_VER2) != 0) {
+		while (((val = sem->_kern._count) & ~SEM_WAITERS) > 0) {
+			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
+				return (0);
+		}
+	} else {
+		while ((val = sem->_kern._count) > 0) {
+			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
+				return (0);
+		}
+	}
+	return (EAGAIN);
+}
+
 int
 _sem_trywait(sem_t *sem)
 {
-	int val;
+	int status;
 
 	if (sem_check_validity(sem) != 0)
 		return (-1);
-
-	while ((val = sem->_kern._count) > 0) {
-		if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
-			return (0);
-	}
-	errno = EAGAIN;
+	if ((status = _trywait(sem)) == 0)
+		return (0);
+	errno = status;
 	return (-1);
 }
 
@@ -389,17 +397,15 @@
 _sem_timedwait(sem_t * __restrict sem,
 	const struct timespec * __restrict abstime)
 {
-	int val, retval;
+	int retval;
 
 	if (sem_check_validity(sem) != 0)
 		return (-1);
 
 	retval = 0;
 	for (;;) {
-		while ((val = sem->_kern._count) > 0) {
-			if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
-				return (0);
-		}
+		if (_trywait(sem) == 0)
+			return (0);
 
 		if (retval) {
 			_pthread_testcancel();
@@ -438,10 +444,36 @@
 int
 _sem_post(sem_t *sem)
 {
+	int count;
 
 	if (sem_check_validity(sem) != 0)
 		return (-1);
 
-	atomic_add_rel_int(&sem->_kern._count, 1);
-	return usem_wake(&sem->_kern);
+	if ((sem->_kern._flags & SEM_VER2) != 0) {
+		for (;;) {
+			count = sem->_kern._count;
+			if ((count & SEM_WAITERS) == 0) {
+				if (__predict_false(count == SEM_VALUE_MAX)) {
+					errno = ERANGE;
+					return (-1);
+				}
+				if (atomic_cmpset_rel_int(&sem->_kern._count, count, count+1))
+					return (0);
+			} else {
+				return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
+			}
+		}
+	} else {
+		do {
+			count = sem->_kern._count;
+			if (__predict_false(count == SEM_VALUE_MAX)) {
+				errno = ERANGE;
+				return (-1);
+			}
+		} while (!atomic_cmpset_rel_int(&sem->_kern._count, count, count+1));
+		rmb();
+		if (!sem->_kern._has_waiters)
+			return (0);
+		return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
+	}
 }