Messages in this thread Patch in this message | | | Subject | [patch] cgroups: disallow attaching kthreadd | From | Mike Galbraith <> | Date | Tue, 03 Apr 2012 19:58:26 +0200 |
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The hazzards of moving kthreadd into a non-root cgroup is still present in mainline. Last go 'round stalled with Peter not liking the cpuset,cpu per controller specific exclusion. I agree that total exclusion is the better option, and below is a respin doing that.
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 <mgalbraith@suse.de> --- kernel/cgroup.c | 20 ++++++++++++++++++++ 1 file changed, 20 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> @@ -1894,6 +1895,14 @@ int cgroup_attach_task(struct cgroup *cg if (tsk->flags & PF_EXITING) return -ESRCH; + /* + * 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) + return -EINVAL; + /* Nothing to do if the task is already in that cgroup */ oldcgrp = task_cgroup_from_root(tsk, root); if (cgrp == oldcgrp) @@ -2172,6 +2181,17 @@ 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) { + ret = -EINVAL; + goto out_unlock_cgroup; + } + get_task_struct(tsk); rcu_read_unlock();
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