From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756861Ab0GIOMZ (ORCPT ); Fri, 9 Jul 2010 10:12:25 -0400 Received: from 101-97.80-90.static-ip.oleane.fr ([90.80.97.101]:36426 "EHLO bohort.kerlabs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754787Ab0GIOMY (ORCPT ); Fri, 9 Jul 2010 10:12:24 -0400 Date: Fri, 9 Jul 2010 16:13:24 +0200 From: Louis Rilling To: "Eric W. Biederman" Cc: Oleg Nesterov , Linux Containers , Andrew Morton , Sukadev Bhattiprolu , linux-kernel@vger.kernel.org, Pavel Emelyanov Subject: Re: [RFC][PATCH 2/2] pidns: Remove proc flush races when a pid namespaces are exiting. Message-ID: <20100709141324.GC18586@hawkmoon.kerlabs.com> Mail-Followup-To: "Eric W. Biederman" , Oleg Nesterov , Linux Containers , Andrew Morton , Sukadev Bhattiprolu , linux-kernel@vger.kernel.org, Pavel Emelyanov References: <20100625102303.GG3773@hawkmoon.kerlabs.com> <20100625183733.GA2627@us.ibm.com> <20100625192945.GA25532@redhat.com> <20100625212618.GA11917@us.ibm.com> <20100625212758.GA30474@redhat.com> <20100625220713.GA31123@us.ibm.com> <20100709121425.GB18586@hawkmoon.kerlabs.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=_bohort-5569-1278684730-0001-2" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a MIME-formatted message. If you see this text it means that your E-mail software does not support MIME-formatted messages. --=_bohort-5569-1278684730-0001-2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 09/07/10 6:05 -0700, Eric W. Biederman wrote: > Louis Rilling writes: >=20 > > On 08/07/10 21:39 -0700, Eric W. Biederman wrote: > >>=20 > >> Currently it is possible to put proc_mnt before we have flushed the > >> last process that will use the proc_mnt to flush it's proc entries. > >>=20 > >> This race is fixed by not flushing proc entries for dead pid > >> namespaces, and calling pid_ns_release_proc unconditionally from > >> zap_pid_ns_processes after the pid namespace has been declared dead. > > > > One comment below. > > > >>=20 > >> To ensure we don't unnecessarily leak any dcache entries with skipped > >> flushes pid_ns_release_proc flushes the entire proc_mnt when it is > >> called. > >>=20 > >> Signed-off-by: Eric W. Biederman > >> --- > >> fs/proc/base.c | 9 +++++---- > >> fs/proc/root.c | 3 +++ > >> kernel/pid_namespace.c | 1 + > >> 3 files changed, 9 insertions(+), 4 deletions(-) > >>=20 > >> diff --git a/fs/proc/base.c b/fs/proc/base.c > >> index acb7ef8..e9d84e1 100644 > >> --- a/fs/proc/base.c > >> +++ b/fs/proc/base.c > >> @@ -2742,13 +2742,14 @@ void proc_flush_task(struct task_struct *task) > >> =20 > >> for (i =3D 0; i <=3D pid->level; i++) { > >> upid =3D &pid->numbers[i]; > >> + > >> + /* Don't bother flushing dead pid namespaces */ > >> + if (test_bit(PIDNS_DEAD, &upid->ns->flags)) > >> + continue; > >> + > > > > IMHO, nothing prevents zap_pid_ns_processes() from setting PIDNS_DEAD a= nd > > calling pid_ns_release_proc() right now. zap_pid_ns_processes() does no= t wait > > for EXIT_DEAD (self-reaping) children to be released. >=20 > Good point we need something probably a lock to prevent proc_mnt from > going away here. We might do a little better if we were starting with > a specific dentry, those at least have some rcu properties but that isn't > a big help. >=20 > Hmm. Perhaps there is a way to completely restructure this flushing > of dentries. It is just an optimization after all so we don't get too ma= ny > stale dentries building up. >=20 > It might just be worth it simply kill proc_flush_mnt altogether. I know > it is measurable when we don't do the flushing but perhaps there can > be a work struct that periodically wakes up and smacks stale proc dentrie= s. >=20 > Right now I really don't think proc_flush_task is worth the hassle it > causes. Indeed, proc_flush_task() seems to be the only bad guy trying to access pid_ns->proc_mnt after the death of the init process. But I don't know enough about the performance impact of removing it. Louis >=20 > Grumble, Grumble more thinking to do. >=20 > Eric > _______________________________________________ > Containers mailing list > Containers@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/containers --=20 Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes --=_bohort-5569-1278684730-0001-2 Content-Type: application/pgp-signature; name="signature.asc" Content-Transfer-Encoding: 7bit Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkw3LoQACgkQVKcRuvQ9Q1TZYwCdF0hDAPJjDiurc9192I0ijLTs FqwAn3L5GDtb4TBeaHFS0PJDeVxVi1Tc =r0qJ -----END PGP SIGNATURE----- --=_bohort-5569-1278684730-0001-2--