Index: libthr/pthread.map
===================================================================
--- libthr/pthread.map	(revision 239227)
+++ libthr/pthread.map	(working copy)
@@ -157,6 +157,7 @@
 	system;
 	tcdrain;
 	usleep;
+	vfork;
 	wait;
 	wait3;
 	wait4;
Index: libthr/thread/thr_vfork.c
===================================================================
--- libthr/thread/thr_vfork.c	(revision 0)
+++ libthr/thread/thr_vfork.c	(working copy)
@@ -0,0 +1,38 @@
+#include "thr_private.h"
+#include <sys/signalvar.h>
+
+extern pid_t __sys_vfork(void);
+
+pid_t _vfork(void);
+
+pid_t
+_vfork(void)
+{
+	struct pthread *curthread = _get_curthread();
+	sigset_t set, oset;
+	pid_t pid;
+
+	SIGFILLSET(set);
+	__sys_sigprocmask(SIG_SETMASK, &set, &oset);
+	if (curthread->vfork == 0)
+		curthread->sigmask = oset;
+	pid = __sys_vfork();
+	if (pid == 0) {
+		curthread->vfork++;
+		__sys_sigprocmask(SIG_SETMASK, &oset, NULL);
+		return (pid);
+	} else if (pid != -1) {
+		/*
+		 * stack was changed by child, we need to
+		 * re-fetch the curthread.
+		 */
+		curthread = _get_curthread();
+		if (curthread->vfork > 0)
+			curthread->vfork--;
+	}
+	if (curthread->vfork == 0)
+		__sys_sigprocmask(SIG_SETMASK, &curthread->sigmask, NULL);
+	return (pid);
+}
+
+__weak_reference(_vfork, vfork);
Index: libthr/thread/thr_sig.c
===================================================================
--- libthr/thread/thr_sig.c	(revision 239227)
+++ libthr/thread/thr_sig.c	(working copy)
@@ -158,9 +158,12 @@
 	int err;
 
 	err = errno;
-	_thr_rwl_rdlock(&_thr_sigact[sig-1].lock);
+	/* no locking for vfork */
+	if (!curthread->vfork)
+		_thr_rwl_rdlock(&_thr_sigact[sig-1].lock);
 	act = _thr_sigact[sig-1].sigact;
-	_thr_rwl_unlock(&_thr_sigact[sig-1].lock);
+	if (!curthread->vfork)
+		_thr_rwl_unlock(&_thr_sigact[sig-1].lock);
 	errno = err;
 
 	/*
@@ -510,6 +513,7 @@
 int
 _sigaction(int sig, const struct sigaction * act, struct sigaction * oact)
 {
+	struct pthread *curthread = _get_curthread();
 	struct sigaction newact, oldact, oldact2;
 	sigset_t oldset;
 	int ret = 0, err = 0;
@@ -522,28 +526,37 @@
 	if (act)
 		newact = *act;
 
-	__sys_sigprocmask(SIG_SETMASK, &_thr_maskset, &oldset);
-	_thr_rwl_wrlock(&_thr_sigact[sig-1].lock);
+	/* no locking for vfork */
+	if (!curthread->vfork) {
+		__sys_sigprocmask(SIG_SETMASK, &_thr_maskset, &oldset);
+		_thr_rwl_wrlock(&_thr_sigact[sig-1].lock);
+	}
  
 	if (act != NULL) {
 		oldact2 = _thr_sigact[sig-1].sigact;
-
- 		/*
-		 * if a new sig handler is SIG_DFL or SIG_IGN,
-		 * don't remove old handler from _thr_sigact[],
-		 * so deferred signals still can use the handlers,
-		 * multiple threads invoking sigaction itself is
-		 * a race condition, so it is not a problem.
-		 */
-		if (newact.sa_handler != SIG_DFL &&
-		    newact.sa_handler != SIG_IGN) {
-			_thr_sigact[sig-1].sigact = newact;
-			remove_thr_signals(
-				&_thr_sigact[sig-1].sigact.sa_mask);
-			newact.sa_flags &= ~SA_NODEFER;
-			newact.sa_flags |= SA_SIGINFO;
-			newact.sa_sigaction = thr_sighandler;
-			newact.sa_mask = _thr_maskset; /* mask all signals */
+		if (curthread->vfork) {
+			/* vfork child can only use SIG_IGN or SIG_DFL */
+			if (newact.sa_handler != SIG_IGN)
+				newact.sa_handler = SIG_DFL;
+		} else {
+ 			/*
+			 * if a new sig handler is SIG_DFL or SIG_IGN,
+			 * don't remove old handler from _thr_sigact[],
+			 * so deferred signals still can use the handlers,
+			 * multiple threads invoking sigaction itself is
+			 * a race condition, so it is not a problem.
+			 */
+			if (newact.sa_handler != SIG_DFL &&
+			    newact.sa_handler != SIG_IGN) {
+				_thr_sigact[sig-1].sigact = newact;
+				remove_thr_signals(
+					&_thr_sigact[sig-1].sigact.sa_mask);
+				newact.sa_flags &= ~SA_NODEFER;
+				newact.sa_flags |= SA_SIGINFO;
+				newact.sa_sigaction = thr_sighandler;
+ 				/* mask all signals */
+				newact.sa_mask = _thr_maskset;
+			}
 		}
 		if ((ret = __sys_sigaction(sig, &newact, &oldact))) {
 			err = errno;
@@ -562,8 +575,10 @@
 			oldact = _thr_sigact[sig-1].sigact;
 	}
 
-	_thr_rwl_unlock(&_thr_sigact[sig-1].lock);
-	__sys_sigprocmask(SIG_SETMASK, &oldset, NULL);
+	if (!curthread->vfork) {
+		_thr_rwl_unlock(&_thr_sigact[sig-1].lock);
+		__sys_sigprocmask(SIG_SETMASK, &oldset, NULL);
+	}
 
 	if (ret == 0) {
 		if (oact != NULL)
Index: libthr/thread/Makefile.inc
===================================================================
--- libthr/thread/Makefile.inc	(revision 239227)
+++ libthr/thread/Makefile.inc	(working copy)
@@ -55,4 +55,5 @@
 	thr_switch_np.c \
 	thr_symbols.c \
 	thr_umtx.c \
+	thr_vfork.c \
 	thr_yield.c
Index: libthr/thread/thr_private.h
===================================================================
--- libthr/thread/thr_private.h	(revision 239227)
+++ libthr/thread/thr_private.h	(working copy)
@@ -523,6 +523,9 @@
 
 	/* Deferred threads from pthread_cond_signal. */
 	unsigned int 		*defer_waiters[MAX_DEFER_WAITERS];
+
+	/* nested vfork count */
+	int			vfork;
 #define _pthread_endzero	wake_addr
 
 	struct wake_addr	*wake_addr;