From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f199.google.com (mail-qk0-f199.google.com [209.85.220.199]) by kanga.kvack.org (Postfix) with ESMTP id E605B6B0005 for ; Mon, 15 Aug 2016 10:37:38 -0400 (EDT) Received: by mail-qk0-f199.google.com with SMTP id i140so121886967qke.0 for ; Mon, 15 Aug 2016 07:37:38 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id l82si15628283wmg.108.2016.08.15.07.37.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Aug 2016 07:37:37 -0700 (PDT) Date: Mon, 15 Aug 2016 10:34:01 -0400 From: Johannes Weiner Subject: Re: [PATCH stable-4.4 1/3] mm: memcontrol: fix cgroup creation failure after many small jobs Message-ID: <20160815143401.GA4796@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> <20160815133748.GA3775@cmpxchg.org> <20160815140439.GF3360@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160815140439.GF3360@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Stable tree , Vladimir Davydov , Andrew Morton , linux-mm@kvack.org, LKML , Nikolay Borisov , Linus Torvalds On Mon, Aug 15, 2016 at 04:04:39PM +0200, Michal Hocko wrote: > 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? Yep, looks good to me. Thanks! -- 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