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SubjectRe: mmotm 2010-04-28 - RCU whinges
David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.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.

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@trash.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@vt.edu>
Tested-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: Patrick McHardy <kaber@trash.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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