From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick McHardy Subject: Re: mmotm 2010-04-28 - RCU whinges Date: Mon, 10 May 2010 17:40:58 +0200 Message-ID: <4BE8290A.2080707@trash.net> 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> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------030908070500050408000807" Cc: 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, paulmck@linux.vnet.ibm.com To: David Miller Return-path: Received: from stinky.trash.net ([213.144.137.162]:48737 "EHLO stinky.trash.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753910Ab0EJPlA (ORCPT ); Mon, 10 May 2010 11:41:00 -0400 In-Reply-To: <20100502.225509.233880079.davem@davemloft.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: This is a multi-part message in MIME format. --------------030908070500050408000807 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 8bit David Miller wrote: > From: Eric Dumazet > Date: Mon, 03 May 2010 07:43:56 +0200 > >> Le lundi 03 mai 2010 à 07:41 +0200, Eric Dumazet a écrit : >> >>> Oops scratch that, I'll resend a correct version. >>> >>> >> Sorry, patch _is_ fine, I had one brain collapse when re-reading it, I >> thought a different mutex was in use in one of the functions. > > Ok, Patrick please review, thanks. Actually we don't need the rcu_dereference() calls at all since registration and unregistration are protected by the mutexes. 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. --------------030908070500050408000807 Content-Type: text/plain; name="x" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="x" commit ed86308f6179d8fa6151c2d0f652aad0091548e2 Author: Patrick McHardy Date: Fri Apr 9 16:42:15 2010 +0200 netfilter: remove invalid rcu_dereference() calls 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. Reported-by: Valdis Kletnieks Tested-by: Valdis Kletnieks Signed-off-by: Patrick McHardy diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_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 = 0; - struct nf_ct_event_notifier *notify; mutex_lock(&nf_ct_ecache_mutex); - notify = rcu_dereference(nf_conntrack_event_cb); - if (notify != NULL) { + if (nf_conntrack_event_cb != NULL) { ret = -EBUSY; goto out_unlock; } @@ -101,11 +99,8 @@ EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier); void nf_conntrack_unregister_notifier(struct nf_ct_event_notifier *new) { - struct nf_ct_event_notifier *notify; - mutex_lock(&nf_ct_ecache_mutex); - notify = rcu_dereference(nf_conntrack_event_cb); - BUG_ON(notify != new); + BUG_ON(nf_conntrack_event_cb != 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_notifier); int nf_ct_expect_register_notifier(struct nf_exp_event_notifier *new) { int ret = 0; - struct nf_exp_event_notifier *notify; mutex_lock(&nf_ct_ecache_mutex); - notify = rcu_dereference(nf_expect_event_cb); - if (notify != NULL) { + if (nf_expect_event_cb != NULL) { ret = -EBUSY; goto out_unlock; } @@ -134,11 +127,8 @@ EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier); 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 = rcu_dereference(nf_expect_event_cb); - BUG_ON(notify != new); + BUG_ON(nf_expect_event_cb != 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, const 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; if (pf >= 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 = rcu_dereference(nf_loggers[pf]); - if (llog == NULL) + if (nf_loggers[pf] == NULL) rcu_assign_pointer(nf_loggers[pf], logger); } @@ -65,13 +63,11 @@ EXPORT_SYMBOL(nf_log_register); void nf_log_unregister(struct nf_logger *logger) { - const struct nf_logger *c_logger; int i; mutex_lock(&nf_log_mutex); for (i = 0; i < ARRAY_SIZE(nf_loggers); i++) { - c_logger = rcu_dereference(nf_loggers[i]); - if (c_logger == logger) + if (nf_loggers[i] == logger) rcu_assign_pointer(nf_loggers[i], NULL); list_del(&logger->list[i]); } --------------030908070500050408000807--