From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 0/1] ns: introduce proc_get_ns_by_fd()
Date: Tue, 29 Sep 2015 20:38:33 +0200
Message-ID: <20150929183833.GA21875@redhat.com>
References: <20150925135246.27620.97496.stgit@buzz> <20150925175654.GA12504@redhat.com> <871tdi8pqj.fsf@x220.int.ebiederm.org> <20150929164315.GA16734@redhat.com> <874mid16bk.fsf@x220.int.ebiederm.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <874mid16bk.fsf-JOvCrm2gF+uungPnsOpG7nhyD016LWXt@public.gmane.org>
Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Konstantin Khlebnikov <khlebnikov-XoJtRXgx1JseBXzfvpsJ4g@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Roman Gushchin <klamm-XoJtRXgx1JseBXzfvpsJ4g@public.gmane.org>, Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>, Chen Fan <chen.fan.fnst-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, =?iso-8859-1?Q?St=E9phane?= Graber <stgraber-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>
List-Id: linux-api@vger.kernel.org

On 09/29, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
>
> > OK, I won't insist, this too looks better to me than proc_ns_fdget(&fd_ref).
> >
> > And in any case fcheck_files() makes more sense than fdget(), somehow I did
> > not think about this when I sent 1/1.
> >
> > Hmm. and after the quick look at cleanup_net() I can't understand whether
> > get_net_ns_by_fd() can use ns_by_fd_rcu() + maybe_get_net(to_net_ns()) or
> > not... Can it?
>
> Some of those places need a reference that allows them to sleep, and the
> code is shared with the legacy pid case so with an addition of get_net
> we can use ns_by_fd_rcu().   There are cases like setns that could
> use ns_by_fd_rcu() with code reording.
>
> We can implement get_net_ns_by_fd as:
> struct net *get_net_ns_by_fd(int fd)
> {
>         struct net *net;
>
> 	rcu_read_lock();
> 	net = net_ns_by_fd_rcu(fd);
>         if (!IS_ERR(net))
>         	get_net(net);
>         rcu_read_unlock();
>
> 	return net;
> }
>
> Which means we can achieve code sharing with the pure rcu version
> as a base.

Yes, this is what I meant... but don't we need maybe_get_net() ?

Oleg.