From: Roman Gushchin <guro@xxxxxx>
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@xxxxxx
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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;
}
_
