Messages in this thread Patch in this message | | | Subject | Re: [resubmit] Re: [patch-final] Re: patch] cpusets, cgroups: disallow attaching kthreadd | From | Mike Galbraith <> | Date | Sat, 07 Jan 2012 07:34:17 +0100 |
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On Fri, 2012-01-06 at 14:06 -0800, Andrew Morton wrote: > On Wed, 07 Dec 2011 05:36:57 +0100 > Mike Galbraith <efault@gmx.de> 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 <efault@gmx.de>
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 <efault@gmx.de> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Paul Menage <paul@paulmenage.org> Cc: Tejun Heo <htejun@gmail.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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 <linux/mutex.h> #include <linux/workqueue.h> #include <linux/cgroup.h> +#include <linux/kthread.h> /* * 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 <linux/ftrace.h> #include <linux/slab.h> #include <linux/init_task.h> +#include <linux/kthread.h> #include <asm/tlb.h> #include <asm/irq_regs.h> @@ -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; }
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