On Wed, Nov 6, 2019 at 2:53 PM Roman Gushchin guro@fb.com 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
Reviewed-by: Shakeel Butt shakeelb@google.com
Cc: stable@vger.kernel.org Cc: Tejun Heo tj@kernel.org
mm/hugetlb_cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c index f1930fa0b445..2ac38bdc18a1 100644 --- a/mm/hugetlb_cgroup.c +++ b/mm/hugetlb_cgroup.c @@ -196,7 +196,7 @@ int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages, 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; }-- 2.17.1