On Wed, Nov 06, 2019 at 02:51:31PM -0800, Roman Gushchin wrote:
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()").
Signed-off-by: Roman Gushchin guro@fb.com Cc: stable@vger.kernel.org Cc: Tejun Heo tj@kernel.org
Acked-by: Tejun Heo tj@kernel.org
Thanks.