Commit 0cd9d33a authored Jan 30, 2020 by Tejun Heo

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



5153faac ("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: 5153faac ("cgroup: remove cgroup_enable_task_cg_lists() optimization")
Cc: stable@vger.kernel.org # v5.5+

parent 39bed42d

kernel/cgroup/cgroup.c

+8 −5

Original line number	Diff line number	Diff line
		@@ -5932,11 +5932,14 @@ void cgroup_post_fork(struct task_struct *child)

		spin_lock_irq(&css_set_lock);

		/* 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

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