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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 12 Feb 2020 12:35:04 -0800
Message-ID: <CAHk-=wi+1CPShMFvJNPfnrJ8DD8uVKUOQ5TQzQUNGLUkeoahkg@mail.gmail.com>
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux Security Module <linux-security-module@vger.kernel.org>,
        Akinobu Mita <akinobu.mita@gmail.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Daniel Micay <danielmicay@gmail.com>,
        Djalal Harouni <tixxdz@gmail.com>,
        "Dmitry V . Levin" <ldv@altlinux.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "J . Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@poochiereds.net>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Solar Designer <solar@openwall.com>
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On Wed, Feb 12, 2020 at 12:03 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> What's to prevent racing with fs shutdown while you are doing the second part?

I was thinking that only the proc_flush_task() code would do this.

And that holds a ref to the vfsmount through upid->ns.

So I wasn't suggesting doing this in general - just splitting up the
implementation of d_invalidate() so that proc_flush_task_mnt() could
delay the complex part to after having traversed the RCU-protected
list.

But hey - I missed this part of the problem originally, so maybe I'm
just missing something else this time. Wouldn't be the first time.

               Linus