On Mon 03-10-22 17:09:15, Alexander Fedorov wrote: > On 03.10.2022 16:32, Michal Hocko wrote: > > On Mon 03-10-22 15:47:10, Alexander Fedorov wrote: > >> @@ -3197,17 +3197,30 @@ static void drain_obj_stock(struct memcg_stock_pcp *stock) > >> stock->nr_bytes = 0; > >> } > >> > >> - obj_cgroup_put(old); > >> + /* > >> + * Clear pointer before freeing memory so that > >> + * drain_all_stock() -> obj_stock_flush_required() > >> + * does not see a freed pointer. > >> + */ > >> stock->cached_objcg = NULL; > >> + obj_cgroup_put(old); > > > > Do we need barrier() or something else to ensure there is no reordering? > > I am not reallyu sure what kind of barriers are implied by the pcp ref > > counting. > > obj_cgroup_put() -> kfree_rcu() -> synchronize_rcu() should take care > of this: This is a very subtle guarantee. Also it would only apply if this is the last reference, right? Is there any reason to not use WRITE_ONCE(stock->cached_objcg, NULL); obj_cgroup_put(old); IIRC this should prevent any reordering. -- Michal Hocko SUSE Labs
