lkml.org 
[lkml]   [2011]   [Oct]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Subjectpatch] cpusets, cgroups: disallow attaching kthreadd
    From
    Date
    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 <efault@gmx.de>

    ---
    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;



    \
     
     \ /
      Last update: 2011-10-18 10:13    [W:0.050 / U:1.176 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site