Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752035AbYJUHdJ (ORCPT ); Tue, 21 Oct 2008 03:33:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751423AbYJUHc5 (ORCPT ); Tue, 21 Oct 2008 03:32:57 -0400 Received: from mtagate4.uk.ibm.com ([195.212.29.137]:56940 "EHLO mtagate4.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751374AbYJUHc4 (ORCPT ); Tue, 21 Oct 2008 03:32:56 -0400 Message-ID: <48FD85A2.8090605@fr.ibm.com> Date: Tue, 21 Oct 2008 09:32:50 +0200 From: Cedric Le Goater User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Li Zefan CC: Andrew Morton , Linux Containers , LKML Subject: Re: [PATCH 2/4] freezer_cg: remove redundant check in freezer_can_attach() References: <48FD26F5.1070809@cn.fujitsu.com> <48FD273F.3040505@cn.fujitsu.com> In-Reply-To: <48FD273F.3040505@cn.fujitsu.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2184 Lines: 66 Li Zefan wrote: > It is sufficient to check if @task is frozen, and no need to check if > the original freezer is frozen. hmm, a task being frozen does not mean that its freezer cgroup is frozen. So the extra check seems valid but looking at the comment : /* * The call to cgroup_lock() in the freezer.state write method prevents * a write to that file racing against an attach, and hence the * can_attach() result will remain valid until the attach completes. */ static int freezer_can_attach(struct cgroup_subsys *ss, how do we know that the task_freezer(task), which is not protected by the cgroup_lock(), is not going to change its state to CGROUP_FROZEN it looks racy. C. > Signed-off-by: Li Zefan > --- > kernel/cgroup_freezer.c | 16 +++++++--------- > 1 files changed, 7 insertions(+), 9 deletions(-) > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c > index 7f54d1c..6fadafe 100644 > --- a/kernel/cgroup_freezer.c > +++ b/kernel/cgroup_freezer.c > @@ -162,9 +162,13 @@ static int freezer_can_attach(struct cgroup_subsys *ss, > struct task_struct *task) > { > struct freezer *freezer; > - int retval; > > - /* Anything frozen can't move or be moved to/from */ > + /* > + * Anything frozen can't move or be moved to/from. > + * > + * Since orig_freezer->state == FROZEN means that @task has been > + * frozen, so it's sufficient to check the latter condition. > + */ > > if (is_task_frozen_enough(task)) > return -EBUSY; > @@ -173,13 +177,7 @@ static int freezer_can_attach(struct cgroup_subsys *ss, > if (freezer->state == CGROUP_FROZEN) > return -EBUSY; > > - retval = 0; > - task_lock(task); > - freezer = task_freezer(task); > - if (freezer->state == CGROUP_FROZEN) > - retval = -EBUSY; > - task_unlock(task); > - return retval; > + return 0; > } > > static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/