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Date:   Wed, 17 Aug 2022 15:19:13 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christian Brauner <brauner@kernel.org>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Dongliang Mu <mudongliangabcd@gmail.com>,
        Dongliang Mu <dzm91@hust.edu.cn>,
        Arve =?iso-8859-1?B?SGr4bm5lduVn?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Carlos Llamas <cmllamas@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Kees Cook <keescook@chromium.org>,
        syzkaller <syzkaller@googlegroups.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] binderfs: rework superblock destruction
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 <20220817140149.pfakskeyxkqcot54@wittgenstein>
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On Wed, Aug 17, 2022 at 04:01:49PM +0200, Christian Brauner wrote:
> On Wed, Aug 17, 2022 at 02:59:02PM +0100, Al Viro wrote:
> > On Wed, Aug 17, 2022 at 03:03:06PM +0200, Christian Brauner wrote:
> > 
> > > +static void binderfs_kill_super(struct super_block *sb)
> > > +{
> > > +	struct binderfs_info *info = sb->s_fs_info;
> > > +
> > > +	if (info && info->ipc_ns)
> > > +		put_ipc_ns(info->ipc_ns);
> > > +
> > > +	kfree(info);
> > > +	kill_litter_super(sb);
> > > +}
> > 
> > Other way round, please - shut the superblock down, *then*
> > free the objects it'd been using.  IOW,
> 
> I wondered about that but a lot of places do it the other way around.
> So maybe the expected order should be documented somewhere.

???

"If you are holding internal references to dentries/inodes/etc., drop them
first; if you are going to free something that is used by filesystem
methods, don't do that before the filesystem is shut down"

That's just common sense...  Which filesystems are doing that "the other
way around"?