Add VB_DUPOK to suppress witness(4) warning of concurrent mount locks.

Use that in three places:
 - vfs_stall()
 - sys_mount()
 - dounmount()'s MNT_FORCE-does-recursive-unmounts case

ok deraadt@ visa@

1 files changed, 7 insertions, 2 deletions

diff --git a/share/man/man9/vfs_busy.9 b/share/man/man9/vfs_busy.9
index a468452e26e..1b6536ea7af 100644
--- a/share/man/man9/vfs_busy.9
+++ b/share/man/man9/vfs_busy.9
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: vfs_busy.9,v 1.2 2007/05/31 19:20:01 jmc Exp $
+.\"	$OpenBSD: vfs_busy.9,v 1.3 2018/06/04 04:57:09 guenther Exp $
 .\"
 .\" Copyright (c) 2006 Nikolay Sturm <sturm@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: May 31 2007 $
+.Dd $Mdocdate: June 4 2018 $
 .Dt VFS_BUSY 9
 .Os
 .Sh NAME
@@ -58,6 +58,10 @@ Acquire a write lock.
 Return immediately; do not wait for the conflicting lock to be released.
 .It VB_WAIT
 Wait for the conflicting lock to be released.
+.It VB_DUPOK
+Prevent
+.Xr witness 4
+from logging when this thread already has a mount point locked.
 .El
 .Pp
 If a conflicting lock was encountered,
@@ -76,5 +80,6 @@ The
 API is implemented in the file
 .Pa sys/kern/vfs_subr.c .
 .Sh SEE ALSO
+.Xr witness 4 ,
 .Xr rwlock 9 ,
 .Xr vfs 9