From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753580Ab1LUR4n (ORCPT ); Wed, 21 Dec 2011 12:56:43 -0500 Received: from mail-we0-f174.google.com ([74.125.82.174]:47001 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744Ab1LUR4k (ORCPT ); Wed, 21 Dec 2011 12:56:40 -0500 Date: Wed, 21 Dec 2011 18:56:35 +0100 From: Frederic Weisbecker To: Oleg Nesterov Cc: Li Zefan , Tejun Heo , LKML , Mandeep Singh Baines , Containers , Cgroups , KAMEZAWA Hiroyuki , Paul Menage , Andrew Morton , "Paul E. McKenney" Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Message-ID: <20111221175632.GF17668@somewhere> References: <20111221034334.GD17668@somewhere> <20111221130848.GA19679@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111221130848.GA19679@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote: > On 12/21, Frederic Weisbecker wrote: > > Hi, > > > > Starring at some parts of cgroups, I have a few questions: > > > > - Is cgroup_enable_task_cg_list()'s while_each_thread() safe > > against concurrent exec()? The leader may change in de_thread() > > and invalidate the test done in while_each_thread(). > > Yes. Oh, we need to do something with while_each_thread. Would something like this work? diff --git a/include/linux/sched.h b/include/linux/sched.h index c0c5876..e002a00 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2293,8 +2293,12 @@ extern bool current_is_single_threaded(void); #define do_each_thread(g, t) \ for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; ) do -#define while_each_thread(g, t) \ - while ((t = next_thread(t)) != g) +#define while_each_thread(g, t) \ + while (({ \ + struct task_struct *__prev = t; \ + t = next_thread(t); \ + t != __prev && t != g; \ + })) static inline int get_nr_threads(struct task_struct *tsk) { From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Date: Wed, 21 Dec 2011 18:56:35 +0100 Message-ID: <20111221175632.GF17668@somewhere> References: <20111221034334.GD17668@somewhere> <20111221130848.GA19679@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=Xka3pwFL26Zi4+RVJ49sWdCbll2QOi+C+3U9j6oF4ZE=; b=KNbUv6UcZx8IEhTkpLrZDwAtrMvX5MQFGSG9WsDd7049U+nVD6geNLLedmJzF+YnUv hyRRFkjvuojuz41Kfv/w+9cgTLjhjhfhXhbLoPQl5jVvNwg70RC8IwRcGQ1BlkS5oWYm XIhQz5lw8D+KI/Jg7bfm9NjKVaiJJ/JbvjX4Y= Content-Disposition: inline In-Reply-To: <20111221130848.GA19679-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Oleg Nesterov Cc: Li Zefan , Tejun Heo , LKML , Mandeep Singh Baines , Containers , Cgroups , KAMEZAWA Hiroyuki , Paul Menage , Andrew Morton , "Paul E. McKenney" On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote: > On 12/21, Frederic Weisbecker wrote: > > Hi, > > > > Starring at some parts of cgroups, I have a few questions: > > > > - Is cgroup_enable_task_cg_list()'s while_each_thread() safe > > against concurrent exec()? The leader may change in de_thread() > > and invalidate the test done in while_each_thread(). > > Yes. Oh, we need to do something with while_each_thread. Would something like this work? diff --git a/include/linux/sched.h b/include/linux/sched.h index c0c5876..e002a00 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2293,8 +2293,12 @@ extern bool current_is_single_threaded(void); #define do_each_thread(g, t) \ for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; ) do -#define while_each_thread(g, t) \ - while ((t = next_thread(t)) != g) +#define while_each_thread(g, t) \ + while (({ \ + struct task_struct *__prev = t; \ + t = next_thread(t); \ + t != __prev && t != g; \ + })) static inline int get_nr_threads(struct task_struct *tsk) {