Index: sys/sys/umtx.h
===================================================================
--- sys/sys/umtx.h	(revision 253951)
+++ sys/sys/umtx.h	(working copy)
@@ -40,10 +40,12 @@
 
 #define	UMUTEX_UNOWNED		0x0
 #define	UMUTEX_CONTESTED	0x80000000U
+#define	UMUTEX_LOCK_BIT		1
 
 #define	UMUTEX_ERROR_CHECK	0x0002	/* Error-checking mutex */
 #define	UMUTEX_PRIO_INHERIT	0x0004	/* Priority inherited mutex */
 #define	UMUTEX_PRIO_PROTECT	0x0008	/* Priority protect mutex */
+#define	UMUTEX_NO_TID		0x0010  /* Do not use thread id */
 
 /* urwlock flags */
 #define URWLOCK_PREFER_READER	0x0002
Index: sys/kern/kern_umtx.c
===================================================================
--- sys/kern/kern_umtx.c	(revision 253951)
+++ sys/kern/kern_umtx.c	(working copy)
@@ -1271,7 +1271,7 @@
 	uint32_t owner, old, id;
 	int error = 0;
 
-	id = td->td_tid;
+	id = (flags & UMUTEX_NO_TID) ? UMUTEX_LOCK_BIT : td->td_tid;
 	uq = td->td_umtxq;
 
 	if (timeout != NULL)
@@ -1394,7 +1394,7 @@
 	int error;
 	int count;
 
-	id = td->td_tid;
+	id = (flags & UMUTEX_NO_TID) ? UMUTEX_LOCK_BIT : td->td_tid;
 	/*
 	 * Make sure we own this mtx.
 	 */
@@ -1402,7 +1402,7 @@
 	if (owner == -1)
 		return (EFAULT);
 
-	if ((owner & ~UMUTEX_CONTESTED) != id)
+	if ((flags & UMUTEX_NO_TID) == 0 && (owner & ~UMUTEX_CONTESTED) != id)
 		return (EPERM);
 
 	if ((owner & UMUTEX_CONTESTED) == 0) {
@@ -1424,23 +1424,38 @@
 	count = umtxq_count(&key);
 	umtxq_unlock(&key);
 
-	/*
-	 * When unlocking the umtx, it must be marked as unowned if
-	 * there is zero or one thread only waiting for it.
-	 * Otherwise, it must be marked as contested.
-	 */
-	old = casuword32(&m->m_owner, owner,
-		count <= 1 ? UMUTEX_UNOWNED : UMUTEX_CONTESTED);
+	for (;;) {
+		if ((flags & UMUTEX_NO_TID) == 0 && (owner & ~UMUTEX_CONTESTED) != id) {
+			error = EINVAL;
+			break;
+		}
+		/*
+		 * When unlocking the umtx, it must be marked as unowned if
+		 * there is zero or one thread only waiting for it.
+		 * Otherwise, it must be marked as contested.
+		 */
+		old = casuword32(&m->m_owner, owner,
+			count <= 1 ? UMUTEX_UNOWNED : UMUTEX_CONTESTED);
+		if (old == -1) {
+			error = EFAULT;
+			break;
+		}
+		if (old == owner)
+			break;
+		error = umtxq_check_susp(td);
+		if (error) {
+			error = ERESTART;
+			break;
+		}
+		owner = old;
+	}
+
 	umtxq_lock(&key);
 	umtxq_signal(&key,1);
 	umtxq_unbusy(&key);
 	umtxq_unlock(&key);
 	umtx_key_release(&key);
-	if (old == -1)
-		return (EFAULT);
-	if (old != owner)
-		return (EINVAL);
-	return (0);
+	return (error);
 }
 
 /*
Index: lib/libthr/thread/thr_mutex.c
===================================================================
--- lib/libthr/thread/thr_mutex.c	(revision 253951)
+++ lib/libthr/thread/thr_mutex.c	(working copy)
@@ -154,7 +154,7 @@
 	switch(attr->m_protocol) {
 	case PTHREAD_PRIO_NONE:
 		pmutex->m_lock.m_owner = UMUTEX_UNOWNED;
-		pmutex->m_lock.m_flags = 0;
+		pmutex->m_lock.m_flags = UMUTEX_NO_TID;
 		break;
 	case PTHREAD_PRIO_INHERIT:
 		pmutex->m_lock.m_owner = UMUTEX_UNOWNED;
@@ -281,6 +281,8 @@
 #define ENQUEUE_MUTEX(curthread, m)  					\
 	do {								\
 		(m)->m_owner = curthread;				\
+		if ((m)->m_lock.m_flags & UMUTEX_NO_TID)		\
+			break;						\
 		/* Add to the list of owned mutexes: */			\
 		MUTEX_ASSERT_NOT_OWNED((m));				\
 		if (((m)->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)	\
@@ -290,7 +292,10 @@
 	} while (0)
 
 #define DEQUEUE_MUTEX(curthread, m)					\
+	do {								\
 		(m)->m_owner = NULL;					\
+		if ((m)->m_lock.m_flags & UMUTEX_NO_TID)		\
+			break;						\
 		MUTEX_ASSERT_IS_OWNED(m);				\
 		if (__predict_true(((m)->m_lock.m_flags & UMUTEX_PRIO_PROTECT) == 0)) \
 			TAILQ_REMOVE(&curthread->mutexq, (m), m_qe);		\
@@ -298,7 +303,8 @@
 			TAILQ_REMOVE(&curthread->pp_mutexq, (m), m_qe);	\
 			set_inherited_priority(curthread, m);		\
 		}							\
-		MUTEX_INIT_LINK(m);
+		MUTEX_INIT_LINK(m);					\
+	} while(0)
 
 #define CHECK_AND_INIT_MUTEX						\
 	if (__predict_false((m = *mutex) <= THR_MUTEX_DESTROYED)) {	\
@@ -319,7 +325,10 @@
 	uint32_t id;
 	int ret;
 
-	id = TID(curthread);
+	if (m->m_lock.m_flags & UMUTEX_NO_TID)
+		id = UMUTEX_LOCK_BIT;
+	else
+		id = TID(curthread);
 	if (m->m_flags & PMUTEX_FLAG_PRIVATE)
 		THR_CRITICAL_ENTER(curthread);
 	ret = _thr_umutex_trylock(&m->m_lock, id);
@@ -354,7 +363,10 @@
 	if (m->m_owner == curthread)
 		return mutex_self_lock(m, abstime);
 
-	id = TID(curthread);
+	if (m->m_lock.m_flags & UMUTEX_NO_TID)
+		id = UMUTEX_LOCK_BIT;
+	else
+		id = TID(curthread);
 	/*
 	 * For adaptive mutexes, spin for a bit in the expectation
 	 * that if the application requests this mutex type then
@@ -416,11 +428,16 @@
 	const struct timespec *abstime, int cvattach)
 {
 	struct pthread *curthread  = _get_curthread();
-	int ret;
+	int ret, id;
 
+	if (m->m_lock.m_flags & UMUTEX_NO_TID)
+		id = UMUTEX_LOCK_BIT;
+	else
+		id = TID(curthread);
+
 	if (!cvattach && m->m_flags & PMUTEX_FLAG_PRIVATE)
 		THR_CRITICAL_ENTER(curthread);
-	if (_thr_umutex_trylock2(&m->m_lock, TID(curthread)) == 0) {
+	if (_thr_umutex_trylock2(&m->m_lock, id) == 0) {
 		ENQUEUE_MUTEX(curthread, m);
 		ret = 0;
 	} else {
@@ -647,7 +664,10 @@
 	if (__predict_false(m->m_owner != curthread))
 		return (EPERM);
 
-	id = TID(curthread);
+	if (m->m_lock.m_flags & UMUTEX_NO_TID)
+		id = UMUTEX_LOCK_BIT;
+	else
+		id = TID(curthread);
 	if (__predict_false(
 		PMUTEX_TYPE(m->m_flags) == PTHREAD_MUTEX_RECURSIVE &&
 		m->m_count > 0)) {