From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754801AbZHFJ66 (ORCPT ); Thu, 6 Aug 2009 05:58:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751361AbZHFJ65 (ORCPT ); Thu, 6 Aug 2009 05:58:57 -0400 Received: from bohort.kerlabs.com ([62.160.40.57]:48814 "EHLO bohort.kerlabs.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751246AbZHFJ64 (ORCPT ); Thu, 6 Aug 2009 05:58:56 -0400 Date: Thu, 6 Aug 2009 11:58:54 +0200 From: Louis Rilling To: Benjamin Blum Cc: Paul Menage , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Peter Zijlstra Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once Message-ID: <20090806095854.GD26446@hawkmoon.kerlabs.com> Mail-Followup-To: Benjamin Blum , Paul Menage , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Peter Zijlstra References: <2f86c2480908031113y525b6cbdhe418b8a0364c7760@mail.gmail.com> <20090803185556.GA8469@us.ibm.com> <20090803194555.GA10158@us.ibm.com> <6599ad830908041148h6d3f3e9bxfef9f3eedec0ab6d@mail.gmail.com> <2f86c2480908041214r1f23c1b7q9a25b04e26c92a1a@mail.gmail.com> <6599ad830908041228w67bc6f7fh57e28f244e1923b3@mail.gmail.com> <20090805102057.GT29252@hawkmoon.kerlabs.com> <6599ad830908050911t6f23f810i65fe8fe17f3ee698@mail.gmail.com> <20090805164218.GB26446@hawkmoon.kerlabs.com> <2f86c2480908051701s57120404q475edbedb58cdca1@mail.gmail.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=_bohort-25455-1249552701-0001-2" Content-Disposition: inline In-Reply-To: <2f86c2480908051701s57120404q475edbedb58cdca1@mail.gmail.com> 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-25455-1249552701-0001-2 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 05/08/09 17:01 -0700, Benjamin Blum wrote: > On Wed, Aug 5, 2009 at 9:42 AM, Louis Rilling = wrote: > > On 05/08/09 =A09:11 -0700, Paul Menage wrote: > >> On Wed, Aug 5, 2009 at 3:20 AM, Louis Rilling wrote: > >> > > >> > The downside of this is teaching lockdep about this recursive lockin= g. Not that > >> > simple actually... > >> > >> Don't we just give each thread's lock its own lock class? That's what > >> we did for the cgroup hierarchy_mutex. > > > > Given that lock classes must be static and that lockdep only supports a= limited > > lock depth, this is an issue for processes having many threads. > > > >> > >> > so that such cases are currently handled using a higher-level > >> > lock that prevents races in locking the whole chain (there was one s= uch example > >> > for locking all vmas with KVM). IIUC, the intent here is to avoid su= ch > >> > higher-level lock. > >> > >> cgroup_mutex already fulfills the role of the higher-level lock. > > > > If so (that is, here cgroup_mutex is taken before write-locking all thr= eads' > > rw_sem), then enhancing rwsem's interface in a similar way to the > > spin_lock_nest_lock() interface could do it. There will still be an iss= ue with > > many threads and lockdep limited lock depth though. >=20 > If we make the locks per-thread, then we can use plain mutexes instead > of rwsems since the only reader will ever be the owning thread itself, > and we can use mutex_lock_nested. mutex_lock_nested is not enough, since this would require putting each thre= ad's mutex in a different class. Again, something like mutex_lock_nest_lock() is the solution, especially since Peter's recent improvement. Louis --=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-25455-1249552701-0001-2 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) iEYEARECAAYFAkp6qV4ACgkQVKcRuvQ9Q1TakgCdGkPpS4VNdOeCy33M1RGh7cUP 2rwAn31xafh5/6FtX2GdvCgM0iv7tIy/ =pleP -----END PGP SIGNATURE----- --=_bohort-25455-1249552701-0001-2--