From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758744Ab0CLWDY (ORCPT ); Fri, 12 Mar 2010 17:03:24 -0500 Received: from e3.ny.us.ibm.com ([32.97.182.143]:53517 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753938Ab0CLWDW (ORCPT ); Fri, 12 Mar 2010 17:03:22 -0500 Date: Fri, 12 Mar 2010 14:03:19 -0800 From: "Paul E. McKenney" To: =?iso-8859-1?Q?Am=E9rico?= Wang Cc: Eric Dumazet , David Miller , peterz@infradead.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: 2.6.34-rc1: rcu lockdep bug? Message-ID: <20100312220319.GC7824@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100311134556.GA6344@linux.vnet.ibm.com> <20100311161751.GA3804@hack> <2375c9f91003112356g1b4164e4pb5f63f0e0e2f310a@mail.gmail.com> <20100312.000705.225033546.davem@davemloft.net> <2375c9f91003120059g771d162fxefc21beb2ab17b4d@mail.gmail.com> <1268392276.3141.4.camel@edumazet-laptop> <2375c9f91003120511j6f33592cl12cb2617a27351ec@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2375c9f91003120511j6f33592cl12cb2617a27351ec@mail.gmail.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 12, 2010 at 09:11:02PM +0800, Américo Wang wrote: > On Fri, Mar 12, 2010 at 7:11 PM, Eric Dumazet wrote: > > Le vendredi 12 mars 2010 à 16:59 +0800, Américo Wang a écrit : > >> On Fri, Mar 12, 2010 at 4:07 PM, David Miller wrote: > >> > From: Américo Wang > >> > Date: Fri, 12 Mar 2010 15:56:03 +0800 > >> > > >> >> Ok, after decoding the lockdep output, it looks like that > >> >> netif_receive_skb() should call rcu_read_lock_bh() instead of rcu_read_lock()? > >> >> But I don't know if all callers of netif_receive_skb() are in softirq context. > >> > > >> > Normally, netif_receive_skb() is invoked from softirq context. > >> > > >> > However, via netpoll it can be invoked essentially from any context. > >> > > >> > But, when this happens, the networking receive path makes amends such > >> > that this works fine.  That's what the netpoll_receive_skb() check in > >> > netif_receive_skb() is for.  That check makes it bail out early if the > >> > call to netif_receive_skb() is via a netpoll invocation. > >> > > >> > >> Oh, I see. This means we should call rcu_read_lock_bh() instead. > >> If Paul has no objections, I will send a patch for this. > >> > > > > Nope, its calling rcu_read_lock() from interrupt context and it should > > stay as is (we dont need to disable bh, this has a cpu cost) > > > > Oh, but lockdep complains about rcu_read_lock(), it said > rcu_read_lock() can't be used in softirq context. > > Am I missing something? Hmmm... It is supposed to be OK to use rcu_read_lock() in pretty much any context, even NMI. I will take a look. Thanx, Paul