mnt: Fix slave mounts order estimation in can_mount_now

For slave mount we need to make sure that all childrent
mountpoints of the master peer is mounted before we can
proceed otherwise there gonna be duplicated mountpoints
after the restore.

https://jira.sw.ru/browse/PSBM-39957Signed-off-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -2125,8 +2125,23 @@ static bool can_mount_now(struct mount_info *mi)
 	if (mi->external)
 		return true;
 
-	if (mi->master_id && mi->bind == NULL)
+	/*
+	 * We're the slave peer:
+	 *   - Make sure the master peer is already mounted
+	 *   - Make sure all children is mounted as well to
+	 *     eliminame mounts duplications
+	 */
+	if (mi->master_id) {
+		struct mount_info *c;
+
+		if (mi->bind == NULL)
+			return false;
+
+		list_for_each_entry(c, &mi->bind->children, siblings) {
+			if (!c->mounted)
 				return false;
+		}
+	}
 
 	if (!fsroot_mounted(mi) && (mi->bind == NULL && !mi->need_plugin && !mi->external))
 		return false;
@@ -2143,9 +2158,6 @@ static bool can_mount_now(struct mount_info *mi)
 			list_for_each_entry(n, &p->mnt_share, mnt_share)
 				if (!n->mounted)
 					return false;
-			list_for_each_entry(n, &p->mnt_slave_list, mnt_slave)
-				if (!n->mounted)
-					return false;
 		}
 	}