From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 97FD46008DF for ; Tue, 24 Aug 2010 04:43:45 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail7.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o7O8hgnT030127 for (envelope-from kamezawa.hiroyu@jp.fujitsu.com); Tue, 24 Aug 2010 17:43:42 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 9E96D45DE51 for ; Tue, 24 Aug 2010 17:43:42 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id 7F25145DD77 for ; Tue, 24 Aug 2010 17:43:42 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 66E801DB8038 for ; Tue, 24 Aug 2010 17:43:42 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id D944A1DB803A for ; Tue, 24 Aug 2010 17:43:38 +0900 (JST) Date: Tue, 24 Aug 2010 17:38:39 +0900 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH] memcg: use ID in page_cgroup Message-Id: <20100824173839.d8285b85.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <20100820185552.426ff12e.kamezawa.hiroyu@jp.fujitsu.com> <20100820190132.43684862.kamezawa.hiroyu@jp.fujitsu.com> <20100824165108.dd986751.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Greg Thelen Cc: linux-mm@kvack.org, "nishimura@mxp.nes.nec.co.jp" , "balbir@linux.vnet.ibm.com" , m-ikeda@ds.jp.nec.com, "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , kamezawa.hiroyuki@gmail.com List-ID: On Tue, 24 Aug 2010 01:35:37 -0700 Greg Thelen wrote: > > rcu_read_lock() is just for delaying to discard object, not for avoiding > > racy updates. All _updates_ requires proper lock or speculative logic as > > atomic_inc_not_zero() etc... Basically, RCU is for avoiding use-after-free. > > > Thanks for the info. Referring to your original patch: > > @@ -2014,11 +2025,11 @@ static int mem_cgroup_move_account(struc > > { > > int ret = -EINVAL; > > lock_page_cgroup(pc); > > - if (PageCgroupUsed(pc) && pc->mem_cgroup == from) { > > + if (PageCgroupUsed(pc) && id_to_memcg(pc->mem_cgroup, true) == from) { > > __mem_cgroup_move_account(pc, from, to, uncharge); > > ret = 0; > > } > > - unlock_page_cgroup(pc); > > + rcu_read_unlock(); > > > > It seems like mem_cgroup_move_account() is not balanced. Why is > lock_page_cgroup(pc) used to lock but rcu_read_unlock() used to unlock? > Nice catch. It's bug. It seems my eyes were corrupted.. Will be fixed in the next version. Sorry for bad code. Thanks, -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/ . Don't email: email@kvack.org