From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633Ab1LUCOW (ORCPT ); Tue, 20 Dec 2011 21:14:22 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:63151 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752519Ab1LUCOT (ORCPT ); Tue, 20 Dec 2011 21:14:19 -0500 Message-ID: <4EF14176.9040206@cn.fujitsu.com> Date: Wed, 21 Dec 2011 10:16:22 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: Frederic Weisbecker CC: Tejun Heo , LKML , Containers , Cgroups , KAMEZAWA Hiroyuki , Oleg Nesterov , Andrew Morton , Paul Menage , Mandeep Singh Baines Subject: Re: [PATCH 2/2 v2] cgroup: Drop task_lock(parent) on cgroup_fork() References: <1324432958-20414-1-git-send-email-fweisbec@gmail.com> <1324432958-20414-3-git-send-email-fweisbec@gmail.com> In-Reply-To: <1324432958-20414-3-git-send-email-fweisbec@gmail.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-12-21 10:13:31, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-12-21 10:13:36, Serialize complete at 2011-12-21 10:13:36 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker wrote: > We don't need to hold the parent task_lock() on the > parent in cgroup_fork() because we are already synchronized > against the two places that may change the parent css_set > concurrently: > > - cgroup_exit(), but the parent obviously can't exit concurrently > - cgroup migration: we are synchronized against threadgroup_lock() > > So we can safely remove the task_lock() there. > > Signed-off-by: Frederic Weisbecker > Cc: Tejun Heo > Cc: Li Zefan > Cc: Containers > Cc: Cgroups > Cc: KAMEZAWA Hiroyuki > Cc: Oleg Nesterov > Cc: Andrew Morton > Cc: Paul Menage > Cc: Mandeep Singh Baines > --- > kernel/cgroup.c | 10 +++++++--- > 1 files changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 24f6d6f..1999f60 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -4556,7 +4556,7 @@ static const struct file_operations proc_cgroupstats_operations = { > * > * A pointer to the shared css_set was automatically copied in > * fork.c by dup_task_struct(). However, we ignore that copy, since > - * it was not made under the protection of RCU or cgroup_mutex, so > + * it was not made under the protection of threadgroup_change_begin(), so I think the original comment still stands, but now threadgroup_change_begin() can also protect the cgroup pointer from becoming invalid. > * might no longer be a valid cgroup pointer. cgroup_attach_task() might > * have already changed current->cgroups, allowing the previously > * referenced cgroup group to be removed and freed. > @@ -4566,10 +4566,14 @@ static const struct file_operations proc_cgroupstats_operations = { > */ > void cgroup_fork(struct task_struct *child) > { > - task_lock(current); > + /* > + * We don't need to task_lock() current because current->cgroups > + * can't be changed concurrently here. The parent obviously hasn't > + * exited and called cgroup_exit(), and we are synchronized against > + * cgroup migration through threadgroup_change_begin(). > + */ > child->cgroups = current->cgroups; > get_css_set(child->cgroups); > - task_unlock(current); > INIT_LIST_HEAD(&child->cg_list); > } > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH 2/2 v2] cgroup: Drop task_lock(parent) on cgroup_fork() Date: Wed, 21 Dec 2011 10:16:22 +0800 Message-ID: <4EF14176.9040206@cn.fujitsu.com> References: <1324432958-20414-1-git-send-email-fweisbec@gmail.com> <1324432958-20414-3-git-send-email-fweisbec@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1324432958-20414-3-git-send-email-fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Frederic Weisbecker Cc: Tejun Heo , LKML , Containers , Cgroups , KAMEZAWA Hiroyuki , Oleg Nesterov , Andrew Morton , Paul Menage , Mandeep Singh Baines Frederic Weisbecker wrote: > We don't need to hold the parent task_lock() on the > parent in cgroup_fork() because we are already synchronized > against the two places that may change the parent css_set > concurrently: > > - cgroup_exit(), but the parent obviously can't exit concurrently > - cgroup migration: we are synchronized against threadgroup_lock() > > So we can safely remove the task_lock() there. > > Signed-off-by: Frederic Weisbecker > Cc: Tejun Heo > Cc: Li Zefan > Cc: Containers > Cc: Cgroups > Cc: KAMEZAWA Hiroyuki > Cc: Oleg Nesterov > Cc: Andrew Morton > Cc: Paul Menage > Cc: Mandeep Singh Baines > --- > kernel/cgroup.c | 10 +++++++--- > 1 files changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 24f6d6f..1999f60 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -4556,7 +4556,7 @@ static const struct file_operations proc_cgroupstats_operations = { > * > * A pointer to the shared css_set was automatically copied in > * fork.c by dup_task_struct(). However, we ignore that copy, since > - * it was not made under the protection of RCU or cgroup_mutex, so > + * it was not made under the protection of threadgroup_change_begin(), so I think the original comment still stands, but now threadgroup_change_begin() can also protect the cgroup pointer from becoming invalid. > * might no longer be a valid cgroup pointer. cgroup_attach_task() might > * have already changed current->cgroups, allowing the previously > * referenced cgroup group to be removed and freed. > @@ -4566,10 +4566,14 @@ static const struct file_operations proc_cgroupstats_operations = { > */ > void cgroup_fork(struct task_struct *child) > { > - task_lock(current); > + /* > + * We don't need to task_lock() current because current->cgroups > + * can't be changed concurrently here. The parent obviously hasn't > + * exited and called cgroup_exit(), and we are synchronized against > + * cgroup migration through threadgroup_change_begin(). > + */ > child->cgroups = current->cgroups; > get_css_set(child->cgroups); > - task_unlock(current); > INIT_LIST_HEAD(&child->cg_list); > } >