From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikolay Aleksandrov Subject: Re: [PATCH net] bonding: fix two race conditions in bond_store_updelay/downdelay Date: Wed, 13 Nov 2013 18:06:34 +0100 Message-ID: <5283B19A.9050302@redhat.com> References: <1384358866-15157-1-git-send-email-nikolay@redhat.com> <1384362214.28458.117.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, davem@davemloft.net, Jay Vosburgh , Andy Gospodarek , Veaceslav Falico To: Eric Dumazet Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6180 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751958Ab3KMRKw (ORCPT ); Wed, 13 Nov 2013 12:10:52 -0500 In-Reply-To: <1384362214.28458.117.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: On 11/13/2013 06:03 PM, Eric Dumazet wrote: > On Wed, 2013-11-13 at 17:07 +0100, Nikolay Aleksandrov wrote: >> This patch fixes two race conditions between bond_store_updelay/downdelay >> and bond_store_miimon which could lead to division by zero as miimon can >> be set to 0 while either updelay/downdelay are being set and thus miss the >> zero check in the beginning, the zero div happens because updelay/downdelay >> are stored as new_value / bond->params.miimon. Use rtnl to synchronize with >> miimon setting. > > It seems a bit heavy duty to take rtnl for this. > > Using ACCESS_ONCE() in bonding_store_updelay()/bonding_store_downdelay() > should be enough ? > > int miimon = ACCESS_ONCE(bond->params.miimon); > > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Hi Eric, I thought about this version too, but downdelay/updelay can be changed in other places (e.g., store_miimon) and the resulting downdelay/updelay value might not be the right one. Correct me if I'm wrong, but this is what I have in mind (miimon = 100, updelay = 200): set miimon to 300 and concurrently set updelay to 400, we might endup leaving updelay to 400 because the old value of miimon is used in the calculation in store_updelay even though when changing miimon updelay/downdelay get adjusted, they might get adjusted by store_updelay/downdelay to a wrong value afterwards. Nik