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SubjectRe: [patch-final] Re: patch] cpusets, cgroups: disallow attaching kthreadd
On Wed, 26 Oct 2011, David Rientjes wrote:

> On Wed, 19 Oct 2011, 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.
> >
> > Signed-off-by: Mike Galbraith <efault@gmx.de>
> > Acked-by: David Rientjes <rientjes@google.com>
> > Acked-by: Paul Menage <paul@paulmenage.org>
> >
>
> Let's add Andrew to the cc so we can get it in -mm, I haven't seen it hit
> linux-next yet.
>

Ping? Still missing from -mm and linux-next.

> > ---
> > 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 <linux/mutex.h>
> > #include <linux/workqueue.h>
> > #include <linux/cgroup.h>
> > +#include <linux/kthread.h>
> >
> > /*
> > * 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 <linux/ctype.h>
> > #include <linux/ftrace.h>
> > #include <linux/slab.h>
> > +#include <linux/kthread.h>
> >
> > #include <asm/tlb.h>
> > #include <asm/irq_regs.h>
> > @@ -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;


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