From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: mmotm 2010-04-28 - RCU whinges Date: Mon, 10 May 2010 08:57:54 -0700 Message-ID: <20100510155754.GB2374@linux.vnet.ibm.com> References: <1272865137.2173.179.camel@edumazet-laptop> <1272865267.2173.180.camel@edumazet-laptop> <1272865436.2173.182.camel@edumazet-laptop> <20100502.225509.233880079.davem@davemloft.net> <4BE8290A.2080707@trash.net> 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: David Miller , eric.dumazet@gmail.com, Valdis.Kletnieks@vt.edu, akpm@linux-foundation.org, peterz@infradead.org, linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org, netdev@vger.kernel.org To: Patrick McHardy Return-path: Content-Disposition: inline In-Reply-To: <4BE8290A.2080707@trash.net> Sender: netdev-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org On Mon, May 10, 2010 at 05:40:58PM +0200, Patrick McHardy wrote: > David Miller wrote: > > From: Eric Dumazet > > Date: Mon, 03 May 2010 07:43:56 +0200 > >=20 > >> Le lundi 03 mai 2010 =E0 07:41 +0200, Eric Dumazet a =E9crit : > >> > >>> Oops scratch that, I'll resend a correct version. > >>> > >>> > >> Sorry, patch _is_ fine, I had one brain collapse when re-reading i= t, I > >> thought a different mutex was in use in one of the functions. > >=20 > > Ok, Patrick please review, thanks. >=20 > Actually we don't need the rcu_dereference() calls at all since > registration and unregistration are protected by the mutexes. The best approach in that case is rcu_dereference_protected() listing the lock that must be held. Of course, your code, so your choice. Thanx, Paul > I queued this patch in nf-next, the only reason why I haven't > submitted it yet is that I was unable to get git to cleanly export > only the proper set of patches meant for -next due to a few merges, > it insists on including 5 patches already merged upstream. If you > don't mind ignoring the first 5 patches in the series, I'll send a > pull request tonight. >=20 >=20 > commit ed86308f6179d8fa6151c2d0f652aad0091548e2 > Author: Patrick McHardy > Date: Fri Apr 9 16:42:15 2010 +0200 >=20 > netfilter: remove invalid rcu_dereference() calls > =20 > The CONFIG_PROVE_RCU option discovered a few invalid uses of > rcu_dereference() in netfilter. In all these cases, the code code > intends to check whether a pointer is already assigned when > performing registration or whether the assigned pointer matches > when performing unregistration. The entire registration/ > unregistration is protected by a mutex, so we don't need the > rcu_dereference() calls. > =20 > Reported-by: Valdis Kletnieks > Tested-by: Valdis Kletnieks > Signed-off-by: Patrick McHardy >=20 > diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_c= onntrack_ecache.c > index d5a9bcd..849614a 100644 > --- a/net/netfilter/nf_conntrack_ecache.c > +++ b/net/netfilter/nf_conntrack_ecache.c > @@ -81,11 +81,9 @@ EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events); > int nf_conntrack_register_notifier(struct nf_ct_event_notifier *new) > { > int ret =3D 0; > - struct nf_ct_event_notifier *notify; >=20 > mutex_lock(&nf_ct_ecache_mutex); > - notify =3D rcu_dereference(nf_conntrack_event_cb); > - if (notify !=3D NULL) { > + if (nf_conntrack_event_cb !=3D NULL) { > ret =3D -EBUSY; > goto out_unlock; > } > @@ -101,11 +99,8 @@ EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier)= ; >=20 > void nf_conntrack_unregister_notifier(struct nf_ct_event_notifier *n= ew) > { > - struct nf_ct_event_notifier *notify; > - > mutex_lock(&nf_ct_ecache_mutex); > - notify =3D rcu_dereference(nf_conntrack_event_cb); > - BUG_ON(notify !=3D new); > + BUG_ON(nf_conntrack_event_cb !=3D new); > rcu_assign_pointer(nf_conntrack_event_cb, NULL); > mutex_unlock(&nf_ct_ecache_mutex); > } > @@ -114,11 +109,9 @@ EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifi= er); > int nf_ct_expect_register_notifier(struct nf_exp_event_notifier *new= ) > { > int ret =3D 0; > - struct nf_exp_event_notifier *notify; >=20 > mutex_lock(&nf_ct_ecache_mutex); > - notify =3D rcu_dereference(nf_expect_event_cb); > - if (notify !=3D NULL) { > + if (nf_expect_event_cb !=3D NULL) { > ret =3D -EBUSY; > goto out_unlock; > } > @@ -134,11 +127,8 @@ EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier= ); >=20 > void nf_ct_expect_unregister_notifier(struct nf_exp_event_notifier *= new) > { > - struct nf_exp_event_notifier *notify; > - > mutex_lock(&nf_ct_ecache_mutex); > - notify =3D rcu_dereference(nf_expect_event_cb); > - BUG_ON(notify !=3D new); > + BUG_ON(nf_expect_event_cb !=3D new); > rcu_assign_pointer(nf_expect_event_cb, NULL); > mutex_unlock(&nf_ct_ecache_mutex); > } > diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c > index 015725a..908f599 100644 > --- a/net/netfilter/nf_log.c > +++ b/net/netfilter/nf_log.c > @@ -35,7 +35,6 @@ static struct nf_logger *__find_logger(int pf, cons= t char *str_logger) > /* return EEXIST if the same logger is registred, 0 on success. */ > int nf_log_register(u_int8_t pf, struct nf_logger *logger) > { > - const struct nf_logger *llog; > int i; >=20 > if (pf >=3D ARRAY_SIZE(nf_loggers)) > @@ -52,8 +51,7 @@ int nf_log_register(u_int8_t pf, struct nf_logger *= logger) > } else { > /* register at end of list to honor first register win */ > list_add_tail(&logger->list[pf], &nf_loggers_l[pf]); > - llog =3D rcu_dereference(nf_loggers[pf]); > - if (llog =3D=3D NULL) > + if (nf_loggers[pf] =3D=3D NULL) > rcu_assign_pointer(nf_loggers[pf], logger); > } >=20 > @@ -65,13 +63,11 @@ EXPORT_SYMBOL(nf_log_register); >=20 > void nf_log_unregister(struct nf_logger *logger) > { > - const struct nf_logger *c_logger; > int i; >=20 > mutex_lock(&nf_log_mutex); > for (i =3D 0; i < ARRAY_SIZE(nf_loggers); i++) { > - c_logger =3D rcu_dereference(nf_loggers[i]); > - if (c_logger =3D=3D logger) > + if (nf_loggers[i] =3D=3D logger) > rcu_assign_pointer(nf_loggers[i], NULL); > list_del(&logger->list[i]); > }