Messages in this thread Patch in this message | | | Subject | Re: [patch] cgroups: disallow attaching kthreadd | From | Mike Galbraith <> | Date | Sat, 21 Apr 2012 07:31:04 +0200 |
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On Fri, 2012-04-20 at 10:57 -0700, Tejun Heo wrote: > Hello, Mike. > > This is dragging out too long but can you please update the patch so > that both kthreadd and PF_THREAD_BOUND tasks are disallowed from !root > cgroups?
cgroups: disallow attaching kthreadd or PF_THREAD_BOUND threads
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 <mgalbraith@suse.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Thomas Gleixner <tglx@linutronix.de> --- kernel/cgroup.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -60,6 +60,7 @@ #include <linux/eventfd.h> #include <linux/poll.h> #include <linux/flex_array.h> /* used in cgroup_attach_proc */ +#include <linux/kthread.h> #include <linux/atomic.h> @@ -2172,6 +2173,17 @@ static int attach_task_by_pid(struct cgr if (threadgroup) tsk = tsk->group_leader; + + /* + * Workqueue threads may acquire PF_THREAD_BOUND and become + * trapped in a cpuset, or RT worker may be born in a cgroup + * with no rt_runtime allocated. Just say no. + */ + if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) { + ret = -EINVAL; + goto out_unlock_cgroup; + } + get_task_struct(tsk); rcu_read_unlock();
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