Messages in this thread Patch in this message | | | Subject | [patch] cpusets, cgroups: disallow attaching kthreadd | From | Mike Galbraith <> | Date | Mon, 10 Oct 2011 10:03:34 +0200 |
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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>
--- 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;
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