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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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