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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>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Mike Galbraith 2012-04-21 09:13:46 +02:00 committed by Tejun Heo
parent 86f82d5618
commit c4c27fbdda
1 changed files with 13 additions and 0 deletions
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13
kernel/cgroup.c
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@ -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>
@ -2225,6 +2226,18 @@ retry_find_task:
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;
rcu_read_unlock();
goto out_unlock_cgroup;
}
get_task_struct(tsk);
rcu_read_unlock();