From 0362f326d86c645b5e96b7dbc3ee515986ed019d Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Fri, 15 Nov 2019 17:34:46 -0800 Subject: [PATCH] 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 Acked-by: Johannes Weiner Acked-by: Tejun Heo Reviewed-by: Shakeel Butt Cc: Michal Hocko Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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; }