From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-eopbgr00136.outbound.protection.outlook.com ([40.107.0.136]:15167 "EHLO EUR02-AM5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751505AbeCTTZn (ORCPT ); Tue, 20 Mar 2018 15:25:43 -0400 Subject: Re: [PATCH net-next v2 2/5] net: Revert "ipv4: fix a deadlock in ip_ra_control" To: David Miller Cc: yoshfuji@linux-ipv6.org, edumazet@google.com, yanhaishuang@cmss.chinamobile.com, nikolay@cumulusnetworks.com, yotamg@mellanox.com, soheil@google.com, avagin@virtuozzo.com, nicolas.dichtel@6wind.com, ebiederm@xmission.com, fw@strlen.de, roman.kapl@sysgo.com, netdev@vger.kernel.org, xiyou.wangcong@gmail.com, dvyukov@google.com, andreyknvl@google.com, lkp@intel.com References: <152145065475.7718.16297762717744383072.stgit@localhost.localdomain> <152145089432.7718.3981942805167545803.stgit@localhost.localdomain> <20180320.122305.1801176841938756457.davem@davemloft.net> From: Kirill Tkhai Message-ID: <41aba98d-6e38-0789-f562-4eada70a84b6@virtuozzo.com> Date: Tue, 20 Mar 2018 22:25:35 +0300 MIME-Version: 1.0 In-Reply-To: <20180320.122305.1801176841938756457.davem@davemloft.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: Hi, David, thanks for the review! On 20.03.2018 19:23, David Miller wrote: > From: Kirill Tkhai > Date: Mon, 19 Mar 2018 12:14:54 +0300 > >> This reverts commit 1215e51edad1. >> Since raw_close() is used on every RAW socket destruction, >> the changes made by 1215e51edad1 scale sadly. This clearly >> seen on endless unshare(CLONE_NEWNET) test, and cleanup_net() >> kwork spends a lot of time waiting for rtnl_lock() introduced >> by this commit. >> >> Next patches in series will rework this in another way, >> so now we revert 1215e51edad1. Also, it doesn't seen >> mrtsock_destruct() takes sk_lock, and the comment to the commit >> does not show the actual stack dump. So, there is a question >> did we really need in it. >> >> Signed-off-by: Kirill Tkhai > > Kirill, I think the commit you are reverting is legitimate. > > The IP_RAW_CONTROL path has an ABBA deadlock with other paths once > you revert this, so you are reintroducing a bug. The talk is about IP_ROUTER_ALERT, I assume there is just an erratum. > All code paths that must take both RTNL and the socket lock must > do them in the same order. And that order is RTNL then socket > lock. The place I change in this patch is IP_ROUTER_ALERT. There is only a call of ip_ra_control(), while this function does not need socket lock. Please, see next patch. It moves this ip_ra_control() out of socket lock. And it fixes the problem pointed in reverted patch in another way. So, if there is ABBA, after next patch it becomes solved. Does this mean I have to merge [2/5] and [3/5] together? > But you are breaking that here by getting us back into a state > where IP_RAW_CONTROL setsockopt will take the socket lock and > then RTNL. > > Again, we can't take, or retake, RTNL if we have the socket lock > currently. > > The only valid locking order is socket lock then RTNL. Thanks, Kirill