Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756261Ab0D0QWH (ORCPT ); Tue, 27 Apr 2010 12:22:07 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:48197 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752498Ab0D0QWF (ORCPT ); Tue, 27 Apr 2010 12:22:05 -0400 Date: Tue, 27 Apr 2010 09:22:01 -0700 From: "Paul E. McKenney" To: "Eric W. Biederman" Cc: Miles Lane , Vivek Goyal , Eric Paris , Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML , nauman@google.com, eric.dumazet@gmail.com, netdev@vger.kernel.org, Jens Axboe , Gui Jianfeng , Li Zefan , Johannes Berg Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage Message-ID: <20100427162201.GA5826@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100422160144.GC2524@linux.vnet.ibm.com> <20100423194255.GE2589@linux.vnet.ibm.com> <20100425023455.GM2440@linux.vnet.ibm.com> <20100426160925.GD2529@linux.vnet.ibm.com> <20100427042744.GD2510@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100427042744.GD2510@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2550 Lines: 64 On Mon, Apr 26, 2010 at 09:27:44PM -0700, Paul E. McKenney wrote: > On Mon, Apr 26, 2010 at 11:35:10AM -0700, Eric W. Biederman wrote: > > "Paul E. McKenney" writes: > > > > > Eric Dumazet traced these down to a commit from Eric Biederman. > > > > > > If I don't hear from Eric Biederman in a few days, I will attempt a > > > patch, but it would be more likely to be correct coming from someone > > > with a better understanding of the code. ;-) > > > > I already replied. > > > > http://lkml.org/lkml/2010/4/21/420 > > You did indeed!!! This experience is giving me an even better appreciation > of the maintainers' ability to keep all their patches straight! > > I will put together something based on your suggestion. How about the following? Thanx, Paul ------------------------------------------------------------------------ commit 85fa42bd568ab99c375f018761ae6345249942cd Author: Paul E. McKenney Date: Mon Apr 26 21:40:05 2010 -0700 net: suppress RCU lockdep false positive in twsk_net() Calls to twsk_net() are in some cases protected by reference counting as an alternative to RCU protection. Cases covered by reference counts include __inet_twsk_kill(), inet_twsk_free(), inet_twdr_do_twkill_work(), inet_twdr_twcal_tick(), and tcp_timewait_state_process(). RCU is used by inet_twsk_purge(). Locking is used by established_get_first() and established_get_next(). Finally, __inet_twsk_hashdance() is an initialization case. It appears to be non-trivial to locate the appropriate locks and reference counts from within twsk_net(), so used rcu_dereference_raw(). Signed-off-by: Paul E. McKenney diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h index 79f67ea..a066fdd 100644 --- a/include/net/inet_timewait_sock.h +++ b/include/net/inet_timewait_sock.h @@ -224,7 +224,9 @@ static inline struct net *twsk_net(const struct inet_timewait_sock *twsk) { #ifdef CONFIG_NET_NS - return rcu_dereference(twsk->tw_net); + return rcu_dereference_raw(twsk->tw_net); /* protected by locking, */ + /* reference counting, */ + /* initialization, or RCU. */ #else return &init_net; #endif -- 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/