From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage Date: Tue, 27 Apr 2010 16:31:11 -0700 Message-ID: <20100427233111.GF2424@linux.vnet.ibm.com> References: <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> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE 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 To: Miles Lane Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Apr 27, 2010 at 01:58:30PM -0400, Miles Lane wrote: > 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= =2E > >> > > > >> > > If I don't hear from Eric Biederman in a few days, I will atte= mpt a > >> > > patch, but it would be more likely to be correct coming from s= omeone > >> > > with a better understanding of the code. =A0;-) > >> > > >> > I already replied. > >> > > >> > http://lkml.org/lkml/2010/4/21/420 > >> > >> You did indeed!!! =A0This experience is giving me an even better a= ppreciation > >> of the maintainers' ability to keep all their patches straight! > >> > >> I will put together something based on your suggestion. > > > > How about the following? > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Thanx, Paul > > > > -------------------------------------------------------------------= ----- > > > > commit 85fa42bd568ab99c375f018761ae6345249942cd > > Author: Paul E. McKenney > > Date: =A0 Mon Apr 26 21:40:05 2010 -0700 > > > > =A0 =A0net: suppress RCU lockdep false positive in twsk_net() > > > > =A0 =A0Calls to twsk_net() are in some cases protected by reference= counting > > =A0 =A0as an alternative to RCU protection. =A0Cases covered by ref= erence counts > > =A0 =A0include __inet_twsk_kill(), inet_twsk_free(), inet_twdr_do_t= wkill_work(), > > =A0 =A0inet_twdr_twcal_tick(), and tcp_timewait_state_process(). =A0= RCU is used > > =A0 =A0by inet_twsk_purge(). =A0Locking is used by established_get_= first() > > =A0 =A0and established_get_next(). =A0Finally, __inet_twsk_hashdanc= e() is an > > =A0 =A0initialization case. > > > > =A0 =A0It appears to be non-trivial to locate the appropriate locks= and > > =A0 =A0reference counts from within twsk_net(), so used rcu_derefer= ence_raw(). > > > > =A0 =A0Signed-off-by: Paul E. McKenney > > > > diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_ti= mewait_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 > > =A0struct net *twsk_net(const struct inet_timewait_sock *twsk) > > =A0{ > > =A0#ifdef CONFIG_NET_NS > > - =A0 =A0 =A0 return rcu_dereference(twsk->tw_net); > > + =A0 =A0 =A0 return rcu_dereference_raw(twsk->tw_net); /* protecte= d by locking, */ > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* reference counting, */ > > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* initialization, or RCU. */ > > =A0#else > > =A0 =A0 =A0 =A0return &init_net; > > =A0#endif > > >=20 > Worked for me. Thanks! Thank you both! I have added Eric's Acked-by and Miles's Tested-by. Thanx, Paul