From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757288Ab1LNUQK (ORCPT ); Wed, 14 Dec 2011 15:16:10 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:56239 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753859Ab1LNUQG (ORCPT ); Wed, 14 Dec 2011 15:16:06 -0500 Date: Wed, 14 Dec 2011 12:16:04 -0800 From: Andrew Morton To: David Rientjes Cc: Mike Galbraith , Paul Menage , LKML , Tejun Heo , Li Zefan , Peter Zijlstra Subject: Re: [resubmit] Re: [patch-final] Re: patch] cpusets, cgroups: disallow attaching kthreadd Message-Id: <20111214121604.bc26ab42.akpm@linux-foundation.org> In-Reply-To: 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> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 7 Dec 2011 14:03:56 -0800 (PST) David Rientjes wrote: > On Wed, 7 Dec 2011, Mike Galbraith wrote: > > > Door #1 with speeling correction. > > > > 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 > > Yes, this looks good. Andrew could you apply this? This patch needed considerable rework resulting from ongoing churn in linux-next cgroups code. It needs checking and retesting, please. From: Mike Galbraith Subject: 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 --- kernel/cpuset.c | 7 +++++-- kernel/sched/core.c | 9 +++++++++ 2 files changed, 14 insertions(+), 2 deletions(-) diff -puN kernel/cpuset.c~cpusets-cgroups-disallow-attaching-kthreadd kernel/cpuset.c --- a/kernel/cpuset.c~cpusets-cgroups-disallow-attaching-kthreadd +++ a/kernel/cpuset.c @@ -59,6 +59,7 @@ #include #include #include +#include /* * Workqueue for cpuset related tasks. @@ -1417,9 +1418,11 @@ static int cpuset_can_attach(struct cgro * 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. + * cpus_allowed may be changed. We also disallow attaching + * kthreadd, to prevent its child from becoming trapped should + * it then acquire PF_THREAD_BOUND. */ - if (task->flags & PF_THREAD_BOUND) + if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task) return -EINVAL; if ((ret = security_task_setscheduler(task))) return ret; diff -puN kernel/sched/core.c~cpusets-cgroups-disallow-attaching-kthreadd kernel/sched/core.c --- a/kernel/sched/core.c~cpusets-cgroups-disallow-attaching-kthreadd +++ a/kernel/sched/core.c @@ -71,6 +71,7 @@ #include #include #include +#include #include #include @@ -7535,6 +7536,14 @@ static int cpu_cgroup_can_attach(struct struct task_struct *task; cgroup_taskset_for_each(task, cgrp, tset) { + /* + * 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), task)) return -EINVAL; _