From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753141AbZHFABt (ORCPT ); Wed, 5 Aug 2009 20:01:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751806AbZHFABt (ORCPT ); Wed, 5 Aug 2009 20:01:49 -0400 Received: from smtp-out.google.com ([216.239.45.13]:1291 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752740AbZHFABs convert rfc822-to-8bit (ORCPT ); Wed, 5 Aug 2009 20:01:48 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: content-type:content-transfer-encoding:x-system-of-record; b=G58XweUyQKktxyRn4ZsVGbh3EX5ntLZY4fXFGdlpukdVdxILpvn489517Nqn7sD3g thfAtRH/YgbNR8qQ6pNlw== MIME-Version: 1.0 In-Reply-To: <20090805164218.GB26446@hawkmoon.kerlabs.com> References: <20090731015154.27908.9639.stgit@hastromil.mtv.corp.google.com> <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> Date: Wed, 5 Aug 2009 17:01:42 -0700 Message-ID: <2f86c2480908051701s57120404q475edbedb58cdca1@mail.gmail.com> Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once From: Benjamin Blum To: Paul Menage , Benjamin Blum , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Peter Zijlstra Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 5, 2009 at 9:42 AM, Louis Rilling wrote: > On 05/08/09  9:11 -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 locking. 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 such example >> > for locking all vmas with KVM). IIUC, the intent here is to avoid such >> > 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 threads' > 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 issue with > many threads and lockdep limited lock depth though. 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. > > Added Peter in CC. > > Louis > > -- > 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 > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.9 (GNU/Linux) > > iEYEARECAAYFAkp5tmoACgkQVKcRuvQ9Q1TwdACeMwdKtGc3rU3PGXPgYvdj9Vxe > xYIAmQFMW6Ri9JGuc7+A0WmGzXkzQ81A > =Wj3u > -----END PGP SIGNATURE----- > >