From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754417Ab1JRIKq (ORCPT ); Tue, 18 Oct 2011 04:10:46 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:45990 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753742Ab1JRIKm (ORCPT ); Tue, 18 Oct 2011 04:10:42 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1+6JIkCqom60Nhn1TI5l91qK6jJGX8fI5gN5erWRJ lADx+eCS2Ak3MV Subject: patch] cpusets, cgroups: disallow attaching kthreadd From: Mike Galbraith To: LKML Cc: Tejun Heo , Li Zefan , Paul Menage , Peter Zijlstra , David Rientjes In-Reply-To: <1318233815.6527.5.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> Content-Type: text/plain; charset="UTF-8" Date: Tue, 18 Oct 2011 10:10:36 +0200 Message-ID: <1318925436.9641.23.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 Mon, 2011-10-10 at 10:03 +0200, Mike Galbraith wrote: > On Mon, 2011-10-10 at 07:34 +0200, Mike Galbraith wrote: > > Maybe the below (which seems to have been stillborn) should be done to > > cgroups as well. Postmortem: kthreadd is attached to a cgroup with no > > rt_runtime allocated, gives birth to severely handicapped kstop threads, > > humongous crash dump follows. > > > > Fiddling with kthreadd is user error, but since it makes no sense to > > move the thing, why not just say no, and save the user's toes some > > needless wear and tear. > > > > > If cpusets doesn't want to let PF_THREAD_BOUND threads out, how about > > > cpusets not letting userland scripts attach kthreadd instead? > > > > > > cpusets: disallow moving kthreadd into a cpuset. > > So how about this, both dirt simple and effective. Ahem, the buildable copy.. I've been asked to add this toe saver to the trees I work on at least until something better comes along. ACK/NACK equally understandable given the infrequency of the toe shooting, and user's right to do so. Off you go, fly or die little patchlet. 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 --- 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;