Subject: Re: mmotm 2010-04-05-16-09 uploaded

From: Patrick McHardy <[email-masked]>
Date: Thu, 08 Apr 2010 13:41:00 +0200

[email-masked] wrote:
> On Mon, 05 Apr 2010 16:09:45 PDT, [email-masked] said:
>> The mm-of-the-moment snapshot 2010-04-05-16-09 has been uploaded to
>>
>>    http://userweb.kernel.org/~akpm/mmotm/
> 
> Seen in dmesg, 2.6.34-rc2-mmotm0323 didn't do this. Tossing it at all the
> likely suspects, hopefully somebody will recognize it and save me the
> bisecting. ;)
> 
> [   11.488535] ctnetlink v0.93: registering with nfnetlink.
> [   11.488579] 
> [   11.488579] ===================================================
> [   11.489529] [ INFO: suspicious rcu_dereference_check() usage. ]
> [   11.489988] ---------------------------------------------------
> [   11.490494] net/netfilter/nf_conntrack_ecache.c:88 invoked rcu_dereference_check() without protection!
> [   11.491024] 
> [   11.491024] other info that might help us debug this:
> [   11.491025] 
> [   11.492834] 
> [   11.492835] rcu_scheduler_active = 1, debug_locks = 0
> [   11.494124] 1 lock held by swapper/1:
> [   11.494776]  #0:  (nf_ct_ecache_mutex){+.+...}, at: [<ffffffff8148c606>] nf_conntrack_register_notifier+0x1a/0x76
> [   11.495505] 

There are some unnecessary rcu_dereference() calls in the conntrack
notifier registration and unregistration functions.

Does this fix it?

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);
 }