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Message-ID: <CAHk-=wi5FOGV_3tALK3n6E2fK3Oa_yCYkYQtCSaXLSEm2DUCKg@mail.gmail.com>
Date:   Wed, 12 Feb 2020 13:02:40 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Security Module <linux-security-module@...r.kernel.org>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances

On Wed, Feb 12, 2020 at 12:41 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Wed, Feb 12, 2020 at 08:38:33PM +0000, Al Viro wrote:
> >
> > Wait, I thought the whole point of that had been to allow multiple
> > procfs instances for the same userns?  Confused...
>
> s/userns/pidns/, sorry

Right, but we still hold the ref to it here...

[ Looks more ]

Oooh. No we don't. Exactly because we don't hold the lock, only the
rcu lifetime, the ref can go away from under us. I see what your
concern is.

Ouch, this is more painful than I expected - the code flow looked so
simple. I really wanted to avoid a new lock during process shutdown,
because that has always been somewhat painful.

            Linus

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