From: Tejun Heo tj@kernel.org
commit 0cd9d33ace336bc424fc30944aa3defd6786e4fe upstream.
5153faac18d2 ("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: 5153faac18d2 ("cgroup: remove cgroup_enable_task_cg_lists() optimization") Cc: stable@vger.kernel.org # v5.5+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/cgroup/cgroup.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)
--- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5932,11 +5932,14 @@ void cgroup_post_fork(struct task_struct
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