Document that our use of pthread_mutex_unlock(3) is async-signal-safe

roy · roy · commit 034d75bffffa · 2014-07-19T14:53:22.000Z
and as such can be used in a phtread_atfork(3) child handler.
diff --git a/lib/libc/gen/arc4random.c b/lib/libc/gen/arc4random.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: arc4random.c,v 1.24 2014/06/12 19:12:19 apb Exp $	*/
+/*	$NetBSD: arc4random.c,v 1.25 2014/07/19 14:53:22 roy Exp $	*/
 /*	$OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $	*/
 
 /*
@@ -27,7 +27,7 @@
 
 #include <sys/cdefs.h>
 #if defined(LIBC_SCCS) && !defined(lint)
-__RCSID("$NetBSD: arc4random.c,v 1.24 2014/06/12 19:12:19 apb Exp $");
+__RCSID("$NetBSD: arc4random.c,v 1.25 2014/07/19 14:53:22 roy Exp $");
 #endif /* LIBC_SCCS and not lint */
 
 #include "namespace.h"
@@ -125,6 +125,12 @@ arc4_fork_child(void)
 static inline void
 arc4_check_init(struct arc4_stream *as)
 {
+	/*
+	 * pthread_atfork(3) only allows async-signal-safe functions in
+	 * the child handler.
+	 * NetBSD's mutex_unlock is async-signal safe, other implementations
+	 * may not be.
+	 */
 
 	if (__predict_false(!as->inited)) {
 		as->inited = true;
diff --git a/lib/libc/gen/pthread_atfork.3 b/lib/libc/gen/pthread_atfork.3
@@ -1,4 +1,4 @@
-.\"	$NetBSD: pthread_atfork.3,v 1.5 2008/04/30 13:10:50 martin Exp $
+.\"	$NetBSD: pthread_atfork.3,v 1.6 2014/07/19 14:53:22 roy Exp $
 .\"
 .\" Copyright (c) 2003 The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd February 12, 2003
+.Dd July 18, 2014
 .Dt PTHREAD_ATFORK 3
 .Os
 .Sh NAME
@@ -91,7 +91,9 @@ The following error code may be returned:
 Insufficient memory exists to register the fork handlers.
 .El
 .Sh SEE ALSO
-.Xr fork 2
+.Xr fork 2 ,
+.Xr pthread_mutex 3 ,
+.Xr signal 7
 .Sh STANDARDS
 The
 .Fn pthread_atfork
@@ -115,6 +117,11 @@ functions are not async-signal-safe, so it is not safe to use such functions
 in the
 .Ar child
 handler.
+POSIX does not mandate that
+.Fn pthread_mutex_unlock
+be async-signal-safe, but it is in NetBSD and thus safe to use within the
+.Ar child
+handler.
 .Sh BUGS
 There is no way to unregister a handler registered with
 .Fn pthread_atfork .
diff --git a/share/man/man7/signal.7 b/share/man/man7/signal.7
@@ -1,4 +1,4 @@
-.\"	$NetBSD: signal.7,v 1.16 2011/01/19 04:33:13 uwe Exp $
+.\"	$NetBSD: signal.7,v 1.17 2014/07/19 14:53:22 roy Exp $
 .\"
 .\" Copyright (c) 1999 The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -24,7 +24,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd February 27, 2009
+.Dd July 18, 2014
 .Dt SIGNAL 7
 .Os
 .Sh NAME
@@ -148,6 +148,7 @@ below is unsafe to use in signal handlers.
 .Xr poll 2 ,
 .\" .Xr posix_trace_event 2
 .\" .Xr pselect 2
+.Xr pthread_mutex_unlock 3 ,
 .Xr raise 3 ,
 .Xr read 2 ,
 .Xr readlink 2 ,
