From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757425Ab1JRKLm (ORCPT ); Tue, 18 Oct 2011 06:11:42 -0400 Received: from mailout-de.gmx.net ([213.165.64.23]:50729 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754379Ab1JRKLl (ORCPT ); Tue, 18 Oct 2011 06:11:41 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1+SWTEHTK2Svb1F9+zcMPpMA22i59Ic+r+Mv1gLEL 759PZaE0S/rYOj Subject: Re: patch] cpusets, cgroups: disallow attaching kthreadd From: Mike Galbraith To: Peter Zijlstra Cc: LKML , Tejun Heo , Li Zefan , Paul Menage , David Rientjes In-Reply-To: <1318929825.9641.32.camel@marge.simson.net> 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> <1318927355.21167.3.camel@twins> <1318927629.9641.27.camel@marge.simson.net> <1318928763.21167.5.camel@twins> <1318929825.9641.32.camel@marge.simson.net> Content-Type: text/plain; charset="UTF-8" Date: Tue, 18 Oct 2011 12:11:33 +0200 Message-ID: <1318932693.6748.5.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-10-18 at 11:23 +0200, Mike Galbraith wrote: > On Tue, 2011-10-18 at 11:06 +0200, Peter Zijlstra wrote: > > On Tue, 2011-10-18 at 10:47 +0200, Mike Galbraith wrote: > > > On Tue, 2011-10-18 at 10:42 +0200, Peter Zijlstra wrote: > > > > > > > Why special case these two, why not simply disallow moving kthreadd into > > > > _any_ cgroup what so ever and be done with it? > > > > > > These were the cases where it hurt, and cpusets don't have to be a > > > component of a cgroup. So we'd still need the cpuset bit. > > > > but but but,, cpusetes are a cgroup thingy?! > > By golly, mount -t cpuset and the thing does say type cgroup. How 'bout > that, learn something new every day. Dinkier is better. From: Peter Zijlstra 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 --- kernel/cgroup.c | 9 +++++++++ 1 file changed, 9 insertions(+) Index: linux-3.0-tip/kernel/cgroup.c =================================================================== --- linux-3.0-tip.orig/kernel/cgroup.c +++ linux-3.0-tip/kernel/cgroup.c @@ -60,6 +60,7 @@ #include #include #include /* used in cgroup_attach_proc */ +#include #include @@ -1824,6 +1825,14 @@ int cgroup_attach_task(struct cgroup *cg struct cgroup *oldcgrp; struct cgroupfs_root *root = cgrp->root; + /* + * Workqueue threads may acquire PF_THREAD_BOUND and become + * trapped in a cpuset, or RT worker may be born in a cgroup + * with no rt_runtime allocated. Just say no. + */ + if (tsk == kthreadd_task) + return -EINVAL; + /* Nothing to do if the task is already in that cgroup */ oldcgrp = task_cgroup_from_root(tsk, root); if (cgrp == oldcgrp)