On Mon 15-08-16 09:37:48, Johannes Weiner wrote: > 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. Ahh, OK, you are right. So I have moved the idr_replace into mem_cgroup_css_alloc. Does the following incremental diff looks better? --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 41fb6a0d2d03..7d6ac40efa81 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4239,12 +4239,6 @@ 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_idr; @@ -4252,13 +4246,16 @@ static struct mem_cgroup *mem_cgroup_alloc(void) if (memcg_wb_domain_init(memcg, GFP_KERNEL)) goto out_free_stat; - idr_replace(&mem_cgroup_idr, memcg, memcg->id.id); + memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL, + 1, MEM_CGROUP_ID_MAX, + GFP_KERNEL); + if (memcg->id.id < 0) + goto out_free_stat; + return memcg; out_free_stat: free_percpu(memcg->stat); -out_idr: - idr_remove(&mem_cgroup_idr, memcg->id.id); out_free: kfree(memcg); return NULL; @@ -4340,9 +4337,11 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) #ifdef CONFIG_CGROUP_WRITEBACK INIT_LIST_HEAD(&memcg->cgwb_list); #endif + idr_replace(&mem_cgroup_idr, memcg, memcg->id.id); return &memcg->css; free_out: + idr_remove(&mem_cgroup_idr, memcg->id.id); __mem_cgroup_free(memcg); return ERR_PTR(error); } -- 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