On Mon, Aug 15, 2016 at 02:46:19PM +0200, Michal Hocko wrote: > On Mon 15-08-16 08:34:07, Johannes Weiner wrote: > > Hi Michal, thanks for doing this. There is only one issue I can see: > > > > On Fri, Aug 12, 2016 at 11:56:17AM +0200, Michal Hocko wrote: > > > @@ -4171,17 +4211,27 @@ static struct mem_cgroup *mem_cgroup_alloc(void) > > > if (!memcg) > > > return NULL; > > > > > > + memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL, > > > + 1, MEM_CGROUP_ID_MAX, > > > + GFP_KERNEL); > > > + if (memcg->id.id < 0) > > > + goto out_free; > > > + > > > memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu); > > > if (!memcg->stat) > > > - goto out_free; > > > + goto out_idr; > > > > > > if (memcg_wb_domain_init(memcg, GFP_KERNEL)) > > > goto out_free_stat; > > > > > > + idr_replace(&mem_cgroup_idr, memcg, memcg->id.id); > > > > This publishes the memcg object too early. Before 4.5, the memcg is > > not fully initialized in mem_cgroup_alloc(). You have to move the > > idr_replace() down to that function (and idr_remove() on free_out). > > You are right. I am just wondering whether it matters. Nobody should see > the id so nobody will be looking it up, no? Page cache shadow entries refer to these IDs weakly. It's possible to refault with a recently recycled memcg ID and crash. That's why we do the whole alloc(NULL) -> replace(memcg) dance in the first place. -- 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