Index: lib/libc/sys/_umtx_op.2
===================================================================
--- lib/libc/sys/_umtx_op.2
+++ lib/libc/sys/_umtx_op.2
@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 13, 2017
+.Dd November 9, 2020
 .Dt _UMTX_OP 2
 .Os
 .Sh NAME
@@ -1124,6 +1124,20 @@
 interruption and
 .Er EINTR
 error.
+.Pp
+If the caller passed in a
+.Fa uaddr
+and
+.Fa uaddr2
+that contain at least enough room for a
+.Vt struct _umtx_time
+followed by a
+.Vt struct timespec ,
+and a relative sleep was interrupted, then the
+.Vt struct timespec
+that follows the initial
+.Fa uaddr2
+is updated to contain the unslept amount.
 .It Dv UMTX_OP_SEM2_WAKE
 Wake up waiters on semaphore lock.
 The arguments to the request are: