| Message ID | 20191106225131.3543616-2-guro@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() | expand |
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> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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 >
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.
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; }
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> --- mm/hugetlb_cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)