[05/11] mm: hugetlb: switch to css_tryget() in hugetlb_cgroup_charge_cgroup()

Commit Message

Andrew Morton Nov. 16, 2019, 1:34 a.m. UTC

From: Roman Gushchin <[e-mail]>
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/[e-mail]
Signed-off-by: Roman Gushchin <[e-mail]>
Acked-by: Johannes Weiner <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- 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;
 	}