From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-fsdevel-owner@vger.kernel.org>
Received: from zeniv.linux.org.uk ([195.92.253.2]:48578 "EHLO
        ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726191AbfACIch (ORCPT
        <rfc822;linux-fsdevel@vger.kernel.org>);
        Thu, 3 Jan 2019 03:32:37 -0500
Date: Thu, 3 Jan 2019 08:32:29 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Andrei Vagin <avagin@gmail.com>
Cc: David Howells <dhowells@redhat.com>, linux-fsdevel@vger.kernel.org,
        cgroups@vger.kernel.org, Li Zefan <lizefan@huawei.com>
Subject: Re: [PATCH vfs/for-next v6] cgroup: fix top cgroup refcnt leak
Message-ID: <20190103083229.GJ2217@ZenIV.linux.org.uk>
References: <20190103010000.GA32003@gmail.com>
 <20190103035426.23526-1-avagin@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190103035426.23526-1-avagin@gmail.com>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Wed, Jan 02, 2019 at 07:54:26PM -0800, Andrei Vagin wrote:

[I'm thoroughly sick of refcounting in that thing, TBH ;-/]

> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index a19f0fec9d82..fe67b5e81f9a 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -2019,7 +2019,7 @@ int cgroup_do_get_tree(struct fs_context *fc)
>  
>  	ret = kernfs_get_tree(fc);
>  	if (ret < 0)
> -		goto out_cgrp;
> +		return ret;

Why does that case avoid needing cgroup_put()?  Note, BTW, that we
also have this:
/*
 * Destroy a cgroup filesystem context.
 */
static void cgroup_fs_context_free(struct fs_context *fc)
{
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);

        kfree(ctx->name);
        kfree(ctx->release_agent);
        if (ctx->root)
                cgroup_put(&ctx->root->cgrp);
        put_cgroup_ns(ctx->ns);
        kernfs_free_fs_context(fc);
        kfree(ctx);
}

which also needs to be taken into account.