On Wed 03-08-16 14:46:40, Vladimir Davydov wrote: > On Wed, Aug 03, 2016 at 01:09:42PM +0200, Michal Hocko wrote: > > On Wed 03-08-16 12:50:49, Vladimir Davydov wrote: > > > 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. > > > > Wouldn't this just paper over a real bug? Anyway I will not insist but > > making the code more complex just to pretend we can handle a situation > > gracefully doesn't sound right to me. > > But we can handle this IMO. AFAICS diverging id refcount will typically > result in leaking swap charges, which aren't even a real resource. Fair enough. > At > worst, we can leak an offline mem_cgroup, which is also not critical > enough to crash the production system. Agreed. > I see your concern of papering over a bug though. What about adding a > warning there? WARN_ON_ONCE sounds better... > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 1c0aa59fd333..8c8e68becee9 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -4044,7 +4044,7 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg) > * The root cgroup cannot be destroyed, so it's refcount must > * always be >= 1. > */ > - if (memcg == root_mem_cgroup) { > + if (WARN_ON_ONCE(memcg == root_mem_cgroup)) { > VM_BUG_ON(1); > break; > } > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a> -- Michal Hocko SUSE Labs -- 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