mount: remove root with MS_PRIVATE before pivot_root

Otherwise if the root is mounted with MS_SHARED, pivot_root fails with EINVAL.
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

mount.c

@@ -603,6 +603,12 @@ static int cr_pivot_root()
 		pr_perror("Can't create a temparary directory");
 		return -1;
 	}
+
+	if (mount("none", "/", "none", MS_REC|MS_PRIVATE, NULL)) {
+		pr_perror("Can't remount root with MS_PRIVATE");
+		return -1;
+	}
+
 	if (pivot_root(".", put_root)) {
 		pr_perror("pivot_root(., %s) failed", put_root);
 		if (rmdir(put_root))

test/zdtm/lib/ns.c

@@ -42,6 +42,12 @@ static int prepare_mntns()
 			fprintf(stderr, "mkdir(old) failed: %m\n");
 			return -1;
 		}
+
+		if (mount("none", "/", "none", MS_REC|MS_PRIVATE, NULL)) {
+			fprintf(stderr, "Can't remount root with MS_PRIVATE: %m\n");
+			return -1;
+		}
+
 		if (pivot_root(".", "./old")) {
 			fprintf(stderr, "pivot_root(., ./old) failed: %m\n");
 			return -1;