- Disable vfs shared locks by default. They must be specifically enabled

on filesystems which safely support them.  It appears that many
   network filesystems specifically are not shared lock safe.

Sponsored by:	Isilon Systems, Inc.

sys/kern/vfs_subr.c

@@ -831,7 +831,11 @@ getnewvnode(tag, mp, vops, vpp)
 	 */
 	vp->v_vnlock = &vp->v_lock;
 	mtx_init(&vp->v_interlock, "vnode interlock", NULL, MTX_DEF);
-	lockinit(vp->v_vnlock, PVFS, tag, VLKTIMEOUT, 0);
+	/*
+	 * By default, don't allow shared locks unless filesystems
+	 * opt-in.
+	 */
+	lockinit(vp->v_vnlock, PVFS, tag, VLKTIMEOUT, LK_NOSHARE);
 	/*
 	 * Initialize bufobj.
 	 */