Messages in this thread | | | Date | Mon, 10 Oct 2011 09:43:39 -0700 | From | Tejun Heo <> | Subject | Re: [patch] cpusets, cgroups: disallow attaching kthreadd |
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Hello,
(cc'ing Thomas and Steven and quoting whole body)
On Mon, Oct 10, 2011 at 10:03:34AM +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. > > 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>
Yes, I think we need something like this. wq workers were using PF_THREAD_BOUND to prevent diddling from userland which made some unhappy. Maybe we need a flag to properly indicate "don't diddle with this thread from userland"? But, then, mainline kernel wouldn't need the current PF_THREAD_BOUND at all. Peter, Steven, what do you think?
Thanks.
> --- > kernel/cpuset.c | 6 ++++-- > kernel/sched.c | 9 +++++++++ > 2 files changed, 13 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 > @@ -9132,6 +9132,15 @@ 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; > >
-- tejun
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