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@

4 files changed, 19 insertions, 8 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
diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index ac6231d0b5f..30e763399cc 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_subr.c,v 1.273 2018/05/27 06:02:14 visa Exp $	*/
+/*	$OpenBSD: vfs_subr.c,v 1.274 2018/06/04 04:57:09 guenther Exp $	*/
 /*	$NetBSD: vfs_subr.c,v 1.53 1996/04/22 01:39:13 christos Exp $	*/
 
 /*
@@ -188,6 +188,11 @@ vfs_busy(struct mount *mp, int flags)
 	else
 		rwflags |= RW_NOSLEEP;
 
+#ifdef WITNESS
+	if (flags & VB_DUPOK)
+		rwflags |= RW_DUPOK;
+#endif
+
 	if (rw_enter(&mp->mnt_lock, rwflags))
 		return (EBUSY);
 
@@ -1602,7 +1607,7 @@ vfs_stall(struct proc *p, int stall)
 	 */
 	TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
 		if (stall) {
-			error = vfs_busy(mp, VB_WRITE|VB_WAIT);
+			error = vfs_busy(mp, VB_WRITE|VB_WAIT|VB_DUPOK);
 			if (error) {
 				printf("%s: busy\n", mp->mnt_stat.f_mntonname);
 				allerror = error;
diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index 7a0571e1353..3c1e28e196a 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vfs_syscalls.c,v 1.284 2018/06/02 10:27:43 mpi Exp $	*/
+/*	$OpenBSD: vfs_syscalls.c,v 1.285 2018/06/04 04:57:09 guenther Exp $	*/
 /*	$NetBSD: vfs_syscalls.c,v 1.71 1996/04/23 10:29:02 mycroft Exp $	*/
 
 /*
@@ -230,7 +230,7 @@ sys_mount(struct proc *p, void *v, register_t *retval)
 
 update:
 	/* Ensure that the parent mountpoint does not get unmounted. */
-	error = vfs_busy(vp->v_mount, VB_READ|VB_NOWAIT);
+	error = vfs_busy(vp->v_mount, VB_READ|VB_NOWAIT|VB_DUPOK);
 	if (error) {
 		if (mp->mnt_flag & MNT_UPDATE) {
 			mp->mnt_flag = mntflag;
@@ -439,7 +439,7 @@ dounmount(struct mount *mp, int flags, struct proc *p)
 				error = EBUSY;
 				goto err;
 			}
-			error = vfs_busy(mp, VB_WRITE|VB_WAIT);
+			error = vfs_busy(mp, VB_WRITE|VB_WAIT|VB_DUPOK);
 			if (error) {
 				if ((flags & MNT_DOOMED)) {
 					/*
diff --git a/sys/sys/mount.h b/sys/sys/mount.h
index 942cb8c8924..2148f7c0449 100644
--- a/sys/sys/mount.h
+++ b/sys/sys/mount.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mount.h,v 1.136 2018/05/08 08:58:49 mpi Exp $	*/
+/*	$OpenBSD: mount.h,v 1.137 2018/06/04 04:57:09 guenther Exp $	*/
 /*	$NetBSD: mount.h,v 1.48 1996/02/18 11:55:47 fvdl Exp $	*/
 
 /*
@@ -564,6 +564,7 @@ int	vfs_busy(struct mount *, int);
 #define VB_WRITE	0x02
 #define VB_NOWAIT	0x04	/* immediately fail on busy lock */
 #define VB_WAIT		0x08	/* sleep fail on busy lock */
+#define VB_DUPOK	0x10	/* permit duplicate mount busying */
 
 int     vfs_isbusy(struct mount *);
 int     vfs_mount_foreach_vnode(struct mount *, int (*func)(struct vnode *,