Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756225Ab0D0R6d (ORCPT ); Tue, 27 Apr 2010 13:58:33 -0400 Received: from mail-px0-f174.google.com ([209.85.212.174]:54135 "EHLO mail-px0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754510Ab0D0R6b convert rfc822-to-8bit (ORCPT ); Tue, 27 Apr 2010 13:58:31 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=a4PQjC3XX0bXGWlyPtk+u40Rg5s4LRcRfsQSCV/umZzeVX8wtxOcxSlL+EQoc29TIO YYsV4rX/2YiXagFeuH0zLF/ry6ETRNU4IxrkRwRZtS/OHJnMAySBwYLb27Usd9mwWZSg EohPqCuAQ6QdiyemzDroCBPdNnkFE0SDTBWsc= MIME-Version: 1.0 In-Reply-To: <20100427162201.GA5826@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> <20100427162201.GA5826@linux.vnet.ibm.com> Date: Tue, 27 Apr 2010 13:58:30 -0400 Message-ID: Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage From: Miles Lane To: paulmck@linux.vnet.ibm.com Cc: "Eric W. Biederman" , 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2893 Lines: 71 On Tue, Apr 27, 2010 at 12:22 PM, Paul E. McKenney wrote: > 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 > Worked for me. Thanks! Miles -- 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/