From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v2] net IPv6 : Fix broken IPv6 routing table after loopback down-up Date: Thu, 28 Mar 2013 12:39:57 -0700 Message-ID: <20130328193957.GH3337@linux.vnet.ibm.com> References: <1364478265.15753.42.camel@edumazet-glaptop> <20130328182356.GE3337@linux.vnet.ibm.com> <1364496577.15753.51.camel@edumazet-glaptop> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Balakumaran Kannan , yoshfuji@linux-ipv6.org, davem@davemloft.net, Patrick McHardy , Alexey Kuznetsov , jmorris@namei.org, Balakumaran.Kannan@ap.sony.com, maruthi.thotad@ap.sony.com, netdev@vger.kernel.org, jamshed.a@ap.sony.com, amit.agarwal@ap.sony.com, takuzo.ohara@jp.sony.com, aaditya.kumar@ap.sony.com To: Eric Dumazet Return-path: Received: from e8.ny.us.ibm.com ([32.97.182.138]:60728 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751145Ab3C1Tku (ORCPT ); Thu, 28 Mar 2013 15:40:50 -0400 Received: from /spool/local by e8.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 28 Mar 2013 15:40:49 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id 6490E38C804F for ; Thu, 28 Mar 2013 15:40:46 -0400 (EDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r2SJej8K347094 for ; Thu, 28 Mar 2013 15:40:45 -0400 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r2SJgdoF031309 for ; Thu, 28 Mar 2013 13:42:41 -0600 Content-Disposition: inline In-Reply-To: <1364496577.15753.51.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Mar 28, 2013 at 11:49:37AM -0700, Eric Dumazet wrote: > On Thu, 2013-03-28 at 11:23 -0700, Paul E. McKenney wrote: > > > > > Agreed, there is no point in using RCU when it is not needed. > > > > That said... > > > > Since v3.1, in CONFIG_PREEMPT=y kernels, rcu_read_lock() does not > > disable preemption. In CONFIG_PREEMPT=n kernels, rcu_read_lock() does > > disable preemption, but to no effect because preemption is already > > disabled anyway. > > > > The net effect is that rcu_read_lock() has no effect on preemption. > > > > Good point, but this patch might be a stable candidate. > > Rule of thumb for networking is > > 1) Control path : RTNL mutex > > 2) Data path : RTNL cant be taken (from softirq), so use RCU if > possible. Stable candidate and rules of thumb sound good to me! Thanx, Paul