From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754661Ab2ADTgd (ORCPT ); Wed, 4 Jan 2012 14:36:33 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:40424 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752506Ab2ADTga (ORCPT ); Wed, 4 Jan 2012 14:36:30 -0500 Date: Wed, 4 Jan 2012 11:36:14 -0800 From: Mandeep Singh Baines To: Oleg Nesterov Cc: Frederic Weisbecker , Mandeep Singh Baines , Li Zefan , Tejun Heo , LKML , Containers , Cgroups , KAMEZAWA Hiroyuki , Paul Menage , Andrew Morton , "Paul E. McKenney" Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Message-ID: <20120104193614.GF9511@google.com> References: <20111221034334.GD17668@somewhere> <20111221130848.GA19679@redhat.com> <20111221175632.GF17668@somewhere> <20111221190102.GE13529@google.com> <20111221190817.GI17668@somewhere> <20111221192413.GF13529@google.com> <20111221200422.GJ17668@somewhere> <20111222153004.GA30522@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111222153004.GA30522@redhat.com> X-Operating-System: Linux/2.6.38.8-gg621 (x86_64) User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov (oleg@redhat.com) wrote: > On 12/21, Frederic Weisbecker wrote: > > > > On Wed, Dec 21, 2011 at 11:24:13AM -0800, Mandeep Singh Baines wrote: > > > > > > If you call exec from a thread other than g, g is now unlinked. So > > > "t != g" will always be true. If you then pthread_create, you now > > > have two threads so "t != __prev" will also always be true. So > > > you now have an infinite loop. > > > > Oh you're right. > > > > But then we can't use t != t->group_leader because that assumes while_each_thread() > > started on the leader. > > Yes, this can't work. > > Besides, we need more burriers to rely on the ->group_leader check. > > See http://marc.info/?t=127688987300002 > I went through the thread. Were there any other concerns other than requiring that you start with the group_leader and the barrier? You could modify zap_other_threads to start with the group leader by skipping p: if (p == t) continue; > in particular, http://marc.info/?l=linux-kernel&m=127714242731448 > I think this should work, but then we should do something with the > users like zap_threads(). > With that patch, won't you potentially miss the exec thread if an exec occurs while you're iterating over the list? Is that OK? Regards, Mandeep > Oleg. > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mandeep Singh Baines Subject: Re: Q: cgroup: Questions about possible issues in cgroup locking Date: Wed, 4 Jan 2012 11:36:14 -0800 Message-ID: <20120104193614.GF9511@google.com> References: <20111221034334.GD17668@somewhere> <20111221130848.GA19679@redhat.com> <20111221175632.GF17668@somewhere> <20111221190102.GE13529@google.com> <20111221190817.GI17668@somewhere> <20111221192413.GF13529@google.com> <20111221200422.GJ17668@somewhere> <20111222153004.GA30522@redhat.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=beta; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:x-operating-system :user-agent; bh=boPKwZdZ6WaRpDuceWWDhrk0R/KeA2y6MDv0yFVksCk=; b=c5VTOFUb57ygnsl1wmAXXIEnLUunsL/osQfxZ6Dk83DOuuO8l+2bXAYXTJKLckwofp 9a2w6xJDEJlJRwX5sw9A== Content-Disposition: inline In-Reply-To: <20111222153004.GA30522-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: Frederic Weisbecker , Mandeep Singh Baines , Li Zefan , Tejun Heo , LKML , Containers , Cgroups , KAMEZAWA Hiroyuki , Paul Menage , Andrew Morton , "Paul E. McKenney" Oleg Nesterov (oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org) wrote: > On 12/21, Frederic Weisbecker wrote: > > > > On Wed, Dec 21, 2011 at 11:24:13AM -0800, Mandeep Singh Baines wrote: > > > > > > If you call exec from a thread other than g, g is now unlinked. So > > > "t != g" will always be true. If you then pthread_create, you now > > > have two threads so "t != __prev" will also always be true. So > > > you now have an infinite loop. > > > > Oh you're right. > > > > But then we can't use t != t->group_leader because that assumes while_each_thread() > > started on the leader. > > Yes, this can't work. > > Besides, we need more burriers to rely on the ->group_leader check. > > See http://marc.info/?t=127688987300002 > I went through the thread. Were there any other concerns other than requiring that you start with the group_leader and the barrier? You could modify zap_other_threads to start with the group leader by skipping p: if (p == t) continue; > in particular, http://marc.info/?l=linux-kernel&m=127714242731448 > I think this should work, but then we should do something with the > users like zap_threads(). > With that patch, won't you potentially miss the exec thread if an exec occurs while you're iterating over the list? Is that OK? Regards, Mandeep > Oleg. >