From: Roman Gushchin guro@fb.com Subject: mm: hugetlb: switch to css_tryget() in hugetlb_cgroup_charge_cgroup()

An exiting task might belong to an offline cgroup. In this case an attempt to grab a cgroup reference from the task can end up with an infinite loop in hugetlb_cgroup_charge_cgroup(), because neither the cgroup will become online, neither the task will be migrated to a live cgroup.

Fix this by switching over to css_tryget(). As css_tryget_online() can't guarantee that the cgroup won't go offline, in most cases the check doesn't make sense. In this particular case users of hugetlb_cgroup_charge_cgroup() are not affected by this change.

A similar problem is described by commit 18fa84a2db0e ("cgroup: Use css_tryget() instead of css_tryget_online() in task_get_css()").

Link: http://lkml.kernel.org/r/20191106225131.3543616-2-guro@fb.com Signed-off-by: Roman Gushchin guro@fb.com Acked-by: Johannes Weiner hannes@cmpxchg.org Acked-by: Tejun Heo tj@kernel.org Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Michal Hocko mhocko@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb_cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/hugetlb_cgroup.c~mm-hugetlb-switch-to-css_tryget-in-hugetlb_cgroup_charge_cgroup +++ a/mm/hugetlb_cgroup.c @@ -196,7 +196,7 @@ int hugetlb_cgroup_charge_cgroup(int idx again: rcu_read_lock(); h_cg = hugetlb_cgroup_from_task(current); - if (!css_tryget_online(&h_cg->css)) { + if (!css_tryget(&h_cg->css)) { rcu_read_unlock(); goto again; } _