Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753895AbZI2Avm (ORCPT ); Mon, 28 Sep 2009 20:51:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753883AbZI2Avk (ORCPT ); Mon, 28 Sep 2009 20:51:40 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:63371 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753694AbZI2Avj (ORCPT ); Mon, 28 Sep 2009 20:51:39 -0400 Message-ID: <4AC159D9.8020900@cn.fujitsu.com> Date: Tue, 29 Sep 2009 08:50:33 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: KAMEZAWA Hiroyuki CC: linux-kernel@vger.kernel.org, "akpm@linux-foundation.org" , mingo@elte.hu, "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" , "menage@google.com" Subject: Re: [PATCH][rc1] cgroup: catch bad css refcnt at css_put References: <200909252158.n8PLwFhG024011@imap1.linux-foundation.org> <20090928154213.8e873dec.kamezawa.hiroyu@jp.fujitsu.com> <20090928180649.b6b7eea9.kamezawa.hiroyu@jp.fujitsu.com> <20090928181310.9492a8a2.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090928181310.9492a8a2.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1898 Lines: 58 KAMEZAWA Hiroyuki wrote: > This is a patch for checking css->refcnt's sanity at css_put(). > > BTW, I noticed that...css->refcnt may overflow if used with memcg... > Now, refcnt is incremented per a page. Paul, do you have any idea ? atomic64_t ? But for 4K pagesize, it won't overflow until when the referenced memory is > 8T? > (Ah, yes. "don't use css->refcnt per page" is maybe reasonable but > it will be big change..) > > == > __css_put() doesn't check a bug as refcnt goes to minus. > I think it should be caught. This patch adds a check for it. > > Signed-off-by: KAMEZAWA Hiroyuki Acked-by: Li Zefan > --- > kernel/cgroup.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > Index: linux-2.6.32-rc1/kernel/cgroup.c > =================================================================== > --- linux-2.6.32-rc1.orig/kernel/cgroup.c > +++ linux-2.6.32-rc1/kernel/cgroup.c > @@ -3708,8 +3708,10 @@ static void check_for_release(struct cgr > void __css_put(struct cgroup_subsys_state *css) > { > struct cgroup *cgrp = css->cgroup; > + int val; > rcu_read_lock(); > - if (atomic_dec_return(&css->refcnt) == 1) { > + val = atomic_dec_return(&css->refcnt); > + if (val == 1) { > if (notify_on_release(cgrp)) { > set_bit(CGRP_RELEASABLE, &cgrp->flags); > check_for_release(cgrp); > @@ -3717,6 +3719,7 @@ void __css_put(struct cgroup_subsys_stat > cgroup_wakeup_rmdir_waiter(cgrp); > } > rcu_read_unlock(); > + WARN_ON(val < 1); When we run into this, it'll probably fill up the syslog quickly, so I think WARN_ON_ONCE() is a bit better. > } > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/