Index: src/share/man/man9/sx.9
===================================================================
--- src/share/man/man9/sx.9	(revision 112)
+++ src/share/man/man9/sx.9	(revision 116)
@@ -43,6 +43,7 @@
 .Nm sx_downgrade ,
 .Nm sx_assert ,
 .Nm sx_unlock ,
+.Nm sx_xlocked ,
 .Nm SX_SYSINIT
 .Nd kernel shared/exclusive lock
 .Sh SYNOPSIS
@@ -71,6 +72,8 @@
 .Fn sx_downgrade "struct sx *sx"
 .Ft void
 .Fn sx_assert "struct sx *sx" "int what"
+.Ft int
+.Fn sx_xlocked "struct sx *sx"
 .\"
 .Ss sx utility macros
 .Fn sx_unlock "struct sx *sx"
@@ -166,6 +169,10 @@
 by the first argument.
 .El
 .Pp
+.Fn sx_xlocked
+will return non-zero if the current process holds the exclusive lock;
+otherwise, it will return zero.
+.Pp
 For ease of programming,
 .Fn sx_unlock
 is provided as a macro frontend to the respective functions,
Index: src/share/man/man9/Makefile
===================================================================
--- src/share/man/man9/Makefile	(revision 112)
+++ src/share/man/man9/Makefile	(revision 116)
@@ -883,7 +883,8 @@
 	sx.9 sx_try_upgrade.9 \
 	sx.9 sx_try_xlock.9 \
 	sx.9 sx_xlock.9 \
-	sx.9 sx_xunlock.9
+	sx.9 sx_xunlock.9 \
+	sx.9 sx_xlocked.9
 MLINKS+=sysctl_add_oid.9 SYSCTL_ADD_INT.9 \
 	sysctl_add_oid.9 SYSCTL_ADD_LONG.9 \
 	sysctl_add_oid.9 SYSCTL_ADD_NODE.9 \
Index: src/sys/kern/kern_sx.c
===================================================================
--- src/sys/kern/kern_sx.c	(revision 112)
+++ src/sys/kern/kern_sx.c	(revision 116)
@@ -367,3 +367,15 @@
 	}
 }
 #endif	/* INVARIANT_SUPPORT */
+
+int
+sx_xlocked(struct sx *sx)
+{
+	mtx_lock(sx->sx_lock);
+	if (sx->sx_xholder == curthread) {
+		mtx_unlock(sx->sx_lock);
+		return (1);
+	}
+	mtx_unlock(sx->sx_lock);
+	return (0);
+}
Index: src/sys/sys/sx.h
===================================================================
--- src/sys/sys/sx.h	(revision 112)
+++ src/sys/sys/sx.h	(revision 116)
@@ -60,6 +60,7 @@
 #ifdef INVARIANT_SUPPORT
 void	_sx_assert(struct sx *sx, int what, const char *file, int line);
 #endif
+int	sx_xlocked(struct sx *sx);
 
 struct sx_args {
 	struct sx 	*sa_sx;