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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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