From mboxrd@z Thu Jan 1 00:00:00 1970 From: Balbir Singh Subject: Re: [-mm] Add an owner to the mm_struct (v7) Date: Fri, 04 Apr 2008 00:04:39 +0530 Message-ID: <47F5233F.1010108@linux.vnet.ibm.com> References: <20080403174433.26356.42121.sendpatchset@localhost.localdomain> <6599ad830804031058l1e2a7ad9p56cff47dca738d79@mail.gmail.com> <47F51DE7.7010204@linux.vnet.ibm.com> <6599ad830804031122y3f6946fbp97dc18073bf02609@mail.gmail.com> Reply-To: balbir@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <6599ad830804031122y3f6946fbp97dc18073bf02609@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Paul Menage Cc: Pavel Emelianov , Hugh Dickins , Sudhir Kumar , YAMAMOTO Takashi , lizf@cn.fujitsu.com, linux-kernel@vger.kernel.org, taka@valinux.co.jp, linux-mm@kvack.org, David Rientjes , Andrew Morton , KAMEZAWA Hiroyuki List-Id: linux-mm.kvack.org Paul Menage wrote: > On Thu, Apr 3, 2008 at 11:11 AM, Balbir Singh wrote: >> > >> > Hmm, is this new check for delay_group_leader() safe? Won't we have >> > called exit_cgroup() by this point, and hence be reassigned to the >> > root cgroup? And so mm->owner->cgroups won't point to the right place? >> > >> >> cgroup_exit() comes in much later after exit_mm(). Moreover delay_group_leader() >> is a function that checks to see if > > Sorry, I was unclear. > > Yes, the call to cgroup_exit() comes much later than exit_mm() - but > it probably does come before the other users of the mm have finished > using the mm. So can't we end up with a situation like this? > > A (group leader) exits; at this point, A->mm->owner == A > A calls exit_mm(), sees delay_group_leader(), doesn't change A->mm->owner > A calls cgroup_exit(), A->cgroups is set to init_css_set. > B (another thread) does something with B->mm->owner->cgroups (e.g. VM > accounting) and accesses the wrong group Hi, Paul, That is indeed quite bad. Do we have to retire the group_leader to init_css_set? Can we not check for delay_group_leader() there? -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL