On Tue, Aug 02, 2016 at 06:00:26PM +0200, Michal Hocko wrote: > On Tue 02-08-16 18:00:48, Vladimir Davydov wrote: ... > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 3be791afd372..4ae12effe347 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -4036,6 +4036,24 @@ static void mem_cgroup_id_get(struct mem_cgroup *memcg) > > atomic_inc(&memcg->id.ref); > > } > > > > +static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg) > > +{ > > + while (!atomic_inc_not_zero(&memcg->id.ref)) { > > + /* > > + * The root cgroup cannot be destroyed, so it's refcount must > > + * always be >= 1. > > + */ > > + if (memcg == root_mem_cgroup) { > > + VM_BUG_ON(1); > > + break; > > + } > > why not simply VM_BUG_ON(memcg == root_mem_cgroup)? Because with DEBUG_VM disabled we could wind up looping forever here if the refcount of the root_mem_cgroup got screwed up. On production kernels, it's better to break the loop and carry on closing eyes on diverging counters rather than getting a lockup. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html