From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751557Ab2AGGei (ORCPT ); Sat, 7 Jan 2012 01:34:38 -0500 Received: from mailout-de.gmx.net ([213.165.64.22]:37718 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751077Ab2AGGeh (ORCPT ); Sat, 7 Jan 2012 01:34:37 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1839bpp4/w3Wb/y39+ILo4VN33N5ezZhoBpePOudn EVBIqzV6PYRchR Subject: Re: [resubmit] Re: [patch-final] Re: patch] cpusets, cgroups: disallow attaching kthreadd From: Mike Galbraith To: Andrew Morton Cc: David Rientjes , Paul Menage , LKML , Tejun Heo , Li Zefan , Peter Zijlstra In-Reply-To: <20120106140625.f5447039.akpm@linux-foundation.org> References: <1316758874.7393.2.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> <20111206144721.7b1d473d.akpm@linux-foundation.org> <1323227914.5057.10.camel@marge.simson.net> <1323232617.5057.50.camel@marge.simson.net> <20120106140625.f5447039.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Date: Sat, 07 Jan 2012 07:34:17 +0100 Message-ID: <1325918057.6514.17.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 Fri, 2012-01-06 at 14:06 -0800, Andrew Morton wrote: > On Wed, 07 Dec 2011 05:36:57 +0100 > 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. > > Someone's been screwing around in linux-next during the merge window. > afacit some patch which was previously there has magically disappeared. > That killed your patch - the original version of the > kernel/sched/core.c chagne applies to the new linux-next but the > kernel/cpuset.c part is all wrecked. Hm, what to do... I can't get to mmotm to see what's there, but fresh pulled linux-next has it as 904655b9, and looked ok. (?) The only thing I can think to do is post it as just plugged into fresh pulled master and hope that helps turn little floundering guppy right side up again. From: Mike Galbraith 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 Cc: Tejun Heo Cc: Li Zefan Cc: Peter Zijlstra Signed-off-by: Andrew Morton diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 0b1712d..cf438f3 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -59,6 +59,7 @@ #include #include #include +#include /* * Workqueue for cpuset related tasks. @@ -1404,9 +1405,10 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont, * 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 a child + * from becoming trapped should it later acquire PF_THREAD_BOUND. */ - if (tsk->flags & PF_THREAD_BOUND) + if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task) return -EINVAL; return 0; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4dbfd04..165d610 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -71,6 +71,7 @@ #include #include #include +#include #include #include @@ -7576,6 +7577,15 @@ cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk) if (tsk->sched_class != &fair_sched_class) return -EINVAL; #endif + /* + * 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; + return 0; }