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cgroup: init_tasks shouldn't be linked to the root cgroup 

5153faac18 ("cgroup: remove cgroup_enable_task_cg_lists()
optimization") removed lazy initialization of css_sets so that new
tasks are always lniked to its css_set. In the process, it incorrectly
ended up adding init_tasks to root css_set. They show up as PID 0's in
root's cgroup.procs triggering warnings in systemd and generally
confusing people.

Fix it by skip css_set linking for init_tasks.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: https://github.com/joanbm
Link: https://github.com/systemd/systemd/issues/14682
Fixes: 5153faac18 ("cgroup: remove cgroup_enable_task_cg_lists() optimization")
Cc: stable@vger.kernel.org # v5.5+
This commit is contained in:
Tejun Heo 2020-01-30 11:37:33 -05:00
parent 39bed42de2
commit 0cd9d33ace
1 changed files with 8 additions and 5 deletions
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13
kernel/cgroup/cgroup.c
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@ -5932,11 +5932,14 @@ void cgroup_post_fork(struct task_struct *child)
spin_lock_irq(&css_set_lock);
WARN_ON_ONCE(!list_empty(&child->cg_list));
cset = task_css_set(current); /* current is @child's parent */
get_css_set(cset);
cset->nr_tasks++;
css_set_move_task(child, NULL, cset, false);
/* init tasks are special, only link regular threads */
if (likely(child->pid)) {
WARN_ON_ONCE(!list_empty(&child->cg_list));
cset = task_css_set(current); /* current is @child's parent */
get_css_set(cset);
cset->nr_tasks++;
css_set_move_task(child, NULL, cset, false);
}
/*
* If the cgroup has to be frozen, the new task has too. Let's set