From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752429Ab1JZU1v (ORCPT ); Wed, 26 Oct 2011 16:27:51 -0400 Received: from smtp-out.google.com ([216.239.44.51]:35275 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751820Ab1JZU1u (ORCPT ); Wed, 26 Oct 2011 16:27:50 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=dkim-signature:date:from:x-x-sender:to:cc:subject: in-reply-to:message-id:references:user-agent:mime-version:content-type:x-system-of-record; b=rDGF7AIt6szlCV4N5s8E6aRoB4yD76KUj4jsBLDIHq338xUyGDn4QSYMMzKyEFoLl JJ/afXdkrH2Kf4Da0b4yQ== Date: Wed, 26 Oct 2011 13:27:45 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Andrew Morton , Mike Galbraith cc: Paul Menage , LKML , Tejun Heo , Li Zefan , Peter Zijlstra Subject: Re: [patch-final] Re: patch] cpusets, cgroups: disallow attaching kthreadd In-Reply-To: <1319001860.6222.34.camel@marge.simson.net> Message-ID: References: <1316758874.7393.2.camel@marge.simson.net> <4E7C2E7F.40307@cn.fujitsu.com> <1316762345.8168.4.camel@marge.simson.net> <1316770936.6641.11.camel@marge.simson.net> <1316775204.7562.9.camel@marge.simson.net> <1316788392.6544.33.camel@marge.simson.net> <1318224892.6161.45.camel@marge.simson.net> <1318233815.6527.5.camel@marge.simson.net> <1318925436.9641.23.camel@marge.simson.net> <1319001860.6222.34.camel@marge.simson.net> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 19 Oct 2011, Mike Galbraith wrote: > cpusets, cgroups: disallow attaching kthreadd > > Allowing kthreadd to be moved to a non-root group makes no sense, it being > a global resource, and needlessly leads unsuspecting users toward trouble. > > 1. An RT workqueue worker thread spawned in a task group with no rt_runtime > allocated is not schedulable. Simple user error, but harmful to the box. > > 2. A worker thread which acquires PF_THREAD_BOUND can never leave a cpuset, > rendering the cpuset immortal. > > Save the user some unexpected trouble, just say no. > > Signed-off-by: Mike Galbraith > Acked-by: David Rientjes > Acked-by: Paul Menage > Let's add Andrew to the cc so we can get it in -mm, I haven't seen it hit linux-next yet. > --- > kernel/cpuset.c | 6 ++++-- > kernel/sched.c | 10 ++++++++++ > 2 files changed, 14 insertions(+), 2 deletions(-) > > Index: linux-3.0-tip/kernel/cpuset.c > =================================================================== > --- linux-3.0-tip.orig/kernel/cpuset.c > +++ linux-3.0-tip/kernel/cpuset.c > @@ -59,6 +59,7 @@ > #include > #include > #include > +#include > > /* > * Workqueue for cpuset related tasks. > @@ -1382,9 +1383,10 @@ static int cpuset_can_attach(struct cgro > * set of allowed nodes is unnecessary. Thus, cpusets are not > * applicable for such threads. This prevents checking for success of > * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may > - * be changed. > + * be changed. We also disallow attaching kthreadd, to prevent it's > + * child from becoming trapped should it then acquire PF_THREAD_BOUND. > */ > - if (tsk->flags & PF_THREAD_BOUND) > + if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task) > return -EINVAL; > > return 0; > Index: linux-3.0-tip/kernel/sched.c > =================================================================== > --- linux-3.0-tip.orig/kernel/sched.c > +++ linux-3.0-tip/kernel/sched.c > @@ -71,6 +71,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -9141,6 +9142,15 @@ cpu_cgroup_destroy(struct cgroup_subsys > static int > cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) > { > + /* > + * kthreadd can fork workers for an RT workqueue in a cgroup > + * which may or may not have rt_runtime allocated. Just say no, > + * as attaching a global resource to a non-root group doesn't > + * make any sense anyway. > + */ > + if (tsk == kthreadd_task) > + return -EINVAL; > + > #ifdef CONFIG_RT_GROUP_SCHED > if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk)) > return -EINVAL;