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Date: Mon, 10 May 2010 08:57:54 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Patrick McHardy <kaber@...sh.net>
Cc: David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
Valdis.Kletnieks@...edu, akpm@...ux-foundation.org,
peterz@...radead.org, linux-kernel@...r.kernel.org,
netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: mmotm 2010-04-28 - RCU whinges
On Mon, May 10, 2010 at 05:40:58PM +0200, Patrick McHardy wrote:
> David Miller wrote:
> > From: Eric Dumazet <eric.dumazet@...il.com>
> > 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.
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.
>
>
> commit ed86308f6179d8fa6151c2d0f652aad0091548e2
> Author: Patrick McHardy <kaber@...sh.net>
> 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 <Valdis.Kletnieks@...edu>
> Tested-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
> Signed-off-by: Patrick McHardy <kaber@...sh.net>
>
> 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]);
> }
--
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