From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx185.postini.com [74.125.245.185]) by kanga.kvack.org (Postfix) with SMTP id 4DB7D6B004F for ; Sun, 4 Dec 2011 21:07:34 -0500 (EST) Received: from m3.gw.fujitsu.co.jp (unknown [10.0.50.73]) by fgwmail5.fujitsu.co.jp (Postfix) with ESMTP id E63EC3EE0C1 for ; Mon, 5 Dec 2011 11:07:32 +0900 (JST) Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id C764C45DEB5 for ; Mon, 5 Dec 2011 11:07:32 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id ACFE645DEBA for ; Mon, 5 Dec 2011 11:07:30 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 9F1DF1DB8038 for ; Mon, 5 Dec 2011 11:07:30 +0900 (JST) Received: from m105.s.css.fujitsu.com (m105.s.css.fujitsu.com [10.240.81.145]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 567E91DB803B for ; Mon, 5 Dec 2011 11:07:30 +0900 (JST) Date: Mon, 5 Dec 2011 11:06:19 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH v7 00/10] Request for Inclusion: per-cgroup tcp memory pressure Message-Id: <20111205110619.ecc538a0.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <4ED91318.1030803@parallels.com> References: <1322611021-1730-1-git-send-email-glommer@parallels.com> <20111130111152.6b1c7366.kamezawa.hiroyu@jp.fujitsu.com> <4ED91318.1030803@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: linux-kernel@vger.kernel.org, paul@paulmenage.org, lizf@cn.fujitsu.com, ebiederm@xmission.com, davem@davemloft.net, gthelen@google.com, netdev@vger.kernel.org, linux-mm@kvack.org, kirill@shutemov.name, avagin@parallels.com, devel@openvz.org, eric.dumazet@gmail.com, cgroups@vger.kernel.org On Fri, 2 Dec 2011 16:04:08 -0200 Glauber Costa wrote: > On 11/30/2011 12:11 AM, KAMEZAWA Hiroyuki wrote: > > On Tue, 29 Nov 2011 21:56:51 -0200 > > Glauber Costa wrote: > > > >> Hi, > >> > >> This patchset implements per-cgroup tcp memory pressure controls. It did not change > >> significantly since last submission: rather, it just merges the comments Kame had. > >> Most of them are style-related and/or Documentation, but there are two real bugs he > >> managed to spot (thanks) > >> > >> Please let me know if there is anything else I should address. > >> > > > > After reading all codes again, I feel some strange. Could you clarify ? > > > > Here. > > == > > +void sock_update_memcg(struct sock *sk) > > +{ > > + /* right now a socket spends its whole life in the same cgroup */ > > + if (sk->sk_cgrp) { > > + WARN_ON(1); > > + return; > > + } > > + if (static_branch(&memcg_socket_limit_enabled)) { > > + struct mem_cgroup *memcg; > > + > > + BUG_ON(!sk->sk_prot->proto_cgroup); > > + > > + rcu_read_lock(); > > + memcg = mem_cgroup_from_task(current); > > + if (!mem_cgroup_is_root(memcg)) > > + sk->sk_cgrp = sk->sk_prot->proto_cgroup(memcg); > > + rcu_read_unlock(); > > == > > > > sk->sk_cgrp is set to a memcg without any reference count. > > > > Then, no check for preventing rmdir() and freeing memcgroup. > > > > Is there some css_get() or mem_cgroup_get() somewhere ? > > > > There were a css_get in the first version of this patchset. It was > removed, however, because it was deemed anti-intuitive to prevent rmdir, > since we can't know which sockets are blocking it, or do anything about > it. Or did I misunderstand something ? > Maybe I misuderstood. Thank you. Ok, there is no css_get/put and rmdir() is allowed. But, hmm....what's guarding threads from stale pointer access ? Does a memory cgroup which is pointed by sk->sk_cgrp always exist ? -Kame -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org