copy_mnt_ns(): use guards

* mntput() of rootmnt and pwdmnt done via __free(mntput)
* mnt_ns_tree_add() can be done within namespace_excl scope.

Signed-off-by: Al Viro <[email protected]>

Author: Al Viro

fs/namespace.c

@@ -4158,7 +4158,8 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 		struct user_namespace *user_ns, struct fs_struct *new_fs)
 {
 	struct mnt_namespace *new_ns;
-	struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
+	struct vfsmount *rootmnt __free(mntput) = NULL;
+	struct vfsmount *pwdmnt __free(mntput) = NULL;
 	struct mount *p, *q;
 	struct mount *old;
 	struct mount *new;
@@ -4177,21 +4178,19 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 	if (IS_ERR(new_ns))
 		return new_ns;
 
-	namespace_lock();
+	guard(namespace_excl)();
 	/* First pass: copy the tree topology */
 	copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
 	if (user_ns != ns->user_ns)
 		copy_flags |= CL_SLAVE;
 	new = copy_tree(old, old->mnt.mnt_root, copy_flags);
 	if (IS_ERR(new)) {
 		emptied_ns = new_ns;
-		namespace_unlock();
 		return ERR_CAST(new);
 	}
 	if (user_ns != ns->user_ns) {
-		lock_mount_hash();
+		guard(mount_writer)();
 		lock_mnt_tree(new);
-		unlock_mount_hash();
 	}
 	new_ns->root = new;
 
@@ -4223,13 +4222,6 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 		while (p->mnt.mnt_root != q->mnt.mnt_root)
 			p = next_mnt(skip_mnt_tree(p), old);
 	}
-	namespace_unlock();
-
-	if (rootmnt)
-		mntput(rootmnt);
-	if (pwdmnt)
-		mntput(pwdmnt);
-
 	mnt_ns_tree_add(new_ns);
 	return new_ns;
 }