From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753021AbcHONlY (ORCPT ); Mon, 15 Aug 2016 09:41:24 -0400 Received: from gum.cmpxchg.org ([85.214.110.215]:58002 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752710AbcHONlW (ORCPT ); Mon, 15 Aug 2016 09:41:22 -0400 Date: Mon, 15 Aug 2016 09:37:48 -0400 From: Johannes Weiner To: Michal Hocko Cc: Stable tree , Vladimir Davydov , Andrew Morton , linux-mm@kvack.org, LKML , Nikolay Borisov , Linus Torvalds Subject: Re: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs Message-ID: <20160815133748.GA3775@cmpxchg.org> References: <1470995779-10064-1-git-send-email-mhocko@kernel.org> <1470995779-10064-2-git-send-email-mhocko@kernel.org> <20160815123407.GA1153@cmpxchg.org> <20160815124615.GD3360@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160815124615.GD3360@dhcp22.suse.cz> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 15 Aug 2016 09:37:48 -0400 From: Johannes Weiner To: Michal Hocko Cc: Stable tree , Vladimir Davydov , Andrew Morton , linux-mm@kvack.org, LKML , Nikolay Borisov , Linus Torvalds Subject: Re: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs Message-ID: <20160815133748.GA3775@cmpxchg.org> References: <1470995779-10064-1-git-send-email-mhocko@kernel.org> <1470995779-10064-2-git-send-email-mhocko@kernel.org> <20160815123407.GA1153@cmpxchg.org> <20160815124615.GD3360@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160815124615.GD3360@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org