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SubjectRe: BUG: atomic counter underflow at ip_conntrack_event_cache_init+0x91/0xb0 (with patch)
Patrick McHardy wrote:
> Mattia Dongili wrote:
>
>>On Mon, Aug 01, 2005 at 04:27:53PM +0200, Patrick McHardy wrote:
>>
>>
>>>>--- include/linux/netfilter_ipv4/ip_conntrack.h.clean 2005-08-01 15:09:49.000000000 +0200
>>>>+++ include/linux/netfilter_ipv4/ip_conntrack.h 2005-08-01 15:08:52.000000000 +0200
>>>>@@ -298,6 +298,7 @@ static inline struct ip_conntrack *
>>>>ip_conntrack_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
>>>>{
>>>> *ctinfo = skb->nfctinfo;
>>>>+ nf_conntrack_get(skb->nfct);
>>>> return (struct ip_conntrack *)skb->nfct;
>>>>}
>>>
>>>This creates lots of refcnt leaks, which is probably why it makes the
>>>underflow go away :) Please try this patch instead.
>>
>>
>>this doesn't fix it actually, see dmesg below:
>
>
> It looks like ip_ct_iterate_cleanup and ip_conntrack_event_cache_init
> race against each other with assigning pointers and grabbing/putting the
> refcounts if called from different contexts.

This should be a fist step towards fixing it. It's probably incomplete
(I'm too tired to check it now), but it should fix the problem you're
seeing. Could you give it a spin?

BTW, ip_ct_iterate_cleanup can only be called from ipt_MASQUERADE when
a device goes down. It seems a bit odd that this is happending on boot,
is there anything special about your setup?

Regards
Patrick
diff --git a/include/linux/netfilter_ipv4/ip_conntrack.h b/include/linux/netfilter_ipv4/ip_conntrack.h
--- a/include/linux/netfilter_ipv4/ip_conntrack.h
+++ b/include/linux/netfilter_ipv4/ip_conntrack.h
@@ -411,6 +411,7 @@ struct ip_conntrack_stat

#ifdef CONFIG_IP_NF_CONNTRACK_EVENTS
#include <linux/notifier.h>
+#include <linux/interrupt.h>

struct ip_conntrack_ecache {
struct ip_conntrack *ct;
@@ -445,26 +446,25 @@ ip_conntrack_expect_unregister_notifier(
return notifier_chain_unregister(&ip_conntrack_expect_chain, nb);
}

+extern void ip_conntrack_event_cache_init(struct ip_conntrack *ct);
+extern void
+ip_conntrack_deliver_cached_events_for(const struct ip_conntrack *ct);
+
static inline void
ip_conntrack_event_cache(enum ip_conntrack_events event,
const struct sk_buff *skb)
{
- struct ip_conntrack_ecache *ecache =
- &__get_cpu_var(ip_conntrack_ecache);
-
- if (unlikely((struct ip_conntrack *) skb->nfct != ecache->ct)) {
- if (net_ratelimit()) {
- printk(KERN_ERR "ctevent: skb->ct != ecache->ct !!!\n");
- dump_stack();
- }
- }
+ struct ip_conntrack *ct = (struct ip_conntrack *)skb->nfct;
+ struct ip_conntrack_ecache *ecache;
+
+ local_bh_disable();
+ ecache = &__get_cpu_var(ip_conntrack_ecache);
+ if (unlikely(ct != ecache->ct))
+ ip_conntrack_event_cache_init(ct);
ecache->events |= event;
+ local_bh_enable();
}

-extern void
-ip_conntrack_deliver_cached_events_for(const struct ip_conntrack *ct);
-extern void ip_conntrack_event_cache_init(const struct sk_buff *skb);
-
static inline void ip_conntrack_event(enum ip_conntrack_events event,
struct ip_conntrack *ct)
{
diff --git a/net/ipv4/netfilter/ip_conntrack_core.c b/net/ipv4/netfilter/ip_conntrack_core.c
--- a/net/ipv4/netfilter/ip_conntrack_core.c
+++ b/net/ipv4/netfilter/ip_conntrack_core.c
@@ -100,56 +100,45 @@ void __ip_ct_deliver_cached_events(struc

/* Deliver all cached events for a particular conntrack. This is called
* by code prior to async packet handling or freeing the skb */
-void
-ip_conntrack_deliver_cached_events_for(const struct ip_conntrack *ct)
+void ip_conntrack_deliver_cached_events_for(const struct ip_conntrack *ct)
{
- struct ip_conntrack_ecache *ecache =
- &__get_cpu_var(ip_conntrack_ecache);
-
- if (!ct)
- return;
-
+ struct ip_conntrack_ecache *ecache;
+
+ local_bh_disable();
+ ecache = &__get_cpu_var(ip_conntrack_ecache);
if (ecache->ct == ct) {
DEBUGP("ecache: delivering event for %p\n", ct);
__deliver_cached_events(ecache);
} else {
- if (net_ratelimit())
- printk(KERN_WARNING "ecache: want to deliver for %p, "
- "but cache has %p\n", ct, ecache->ct);
+ DEBUGP("ecache: already delivered for %p, cache %p",
+ ct, ecache->ct);
}
-
/* signalize that events have already been delivered */
ecache->ct = NULL;
+ local_bh_enable();
}

/* Deliver cached events for old pending events, if current conntrack != old */
-void ip_conntrack_event_cache_init(const struct sk_buff *skb)
+void ip_conntrack_event_cache_init(struct ip_conntrack *ct)
{
- struct ip_conntrack *ct = (struct ip_conntrack *) skb->nfct;
- struct ip_conntrack_ecache *ecache =
- &__get_cpu_var(ip_conntrack_ecache);
+ struct ip_conntrack_ecache *ecache;

/* take care of delivering potentially old events */
- if (ecache->ct != ct) {
- enum ip_conntrack_info ctinfo;
- /* we have to check, since at startup the cache is NULL */
- if (likely(ecache->ct)) {
- DEBUGP("ecache: entered for different conntrack: "
- "ecache->ct=%p, skb->nfct=%p. delivering "
- "events\n", ecache->ct, ct);
- __deliver_cached_events(ecache);
- ip_conntrack_put(ecache->ct);
- } else {
- DEBUGP("ecache: entered for conntrack %p, "
- "cache was clean before\n", ct);
- }
-
- /* initialize for this conntrack/packet */
- ecache->ct = ip_conntrack_get(skb, &ctinfo);
- /* ecache->events cleared by __deliver_cached_devents() */
+ ecache = &__get_cpu_var(ip_conntrack_ecache);
+ BUG_ON(ecache->ct == ct);
+ if (ecache->ct) {
+ DEBUGP("ecache: entered for different conntrack: "
+ "ecache->ct=%p, skb->nfct=%p. delivering "
+ "events\n", ecache->ct, ct);
+ __deliver_cached_events(ecache);
+ ip_conntrack_put(ecache->ct);
} else {
- DEBUGP("ecache: re-entered for conntrack %p.\n", ct);
+ DEBUGP("ecache: entered for conntrack %p, "
+ "cache was clean before\n", ct);
}
+ /* initialize for this conntrack/packet */
+ ecache->ct = ct;
+ nf_conntrack_get(&ct->ct_general);
}

#endif /* CONFIG_IP_NF_CONNTRACK_EVENTS */
@@ -873,8 +862,6 @@ unsigned int ip_conntrack_in(unsigned in

IP_NF_ASSERT((*pskb)->nfct);

- ip_conntrack_event_cache_init(*pskb);
-
ret = proto->packet(ct, *pskb, ctinfo);
if (ret < 0) {
/* Invalid: inverse of the return code tells
@@ -1279,15 +1266,18 @@ ip_ct_iterate_cleanup(int (*iter)(struct
/* we need to deliver all cached events in order to drop
* the reference counts */
int cpu;
+
+ local_bh_disable();
for_each_cpu(cpu) {
struct ip_conntrack_ecache *ecache =
&per_cpu(ip_conntrack_ecache, cpu);
if (ecache->ct) {
- __ip_ct_deliver_cached_events(ecache);
+ __deliver_cached_events(ecache);
ip_conntrack_put(ecache->ct);
ecache->ct = NULL;
}
}
+ local_bh_enable();
}
#endif
}
diff --git a/net/ipv4/netfilter/ip_conntrack_standalone.c b/net/ipv4/netfilter/ip_conntrack_standalone.c
--- a/net/ipv4/netfilter/ip_conntrack_standalone.c
+++ b/net/ipv4/netfilter/ip_conntrack_standalone.c
@@ -401,9 +401,13 @@ static unsigned int ip_confirm(unsigned
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
- ip_conntrack_event_cache_init(*pskb);
/* We've seen it coming out the other side: confirm it */
- return ip_conntrack_confirm(pskb);
+ struct ip_conntrack *ct = (struct ip_conntrack *)(*pskb)->nfct;
+ unsigned int ret;
+
+ ret = ip_conntrack_confirm(pskb);
+ ip_conntrack_deliver_cached_events_for(ct);
+ return ret;
}

static unsigned int ip_conntrack_help(unsigned int hooknum,
@@ -419,7 +423,7 @@ static unsigned int ip_conntrack_help(un
ct = ip_conntrack_get(*pskb, &ctinfo);
if (ct && ct->helper) {
unsigned int ret;
- ip_conntrack_event_cache_init(*pskb);
+ ip_conntrack_event_cache_init(ct);
ret = ct->helper->help(pskb, ct, ctinfo);
if (ret != NF_ACCEPT)
return ret;
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