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netfilter: nf_conncount: reduce unnecessary GC

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Currently nf_conncount can trigger garbage collection (GC)
at multiple places. Each GC process takes a spin_lock_bh
to traverse the nf_conncount_list. We found that when testing
port scanning use two parallel nmap, because the number of
connection increase fast, the nf_conncount_count and its
subsequent call to __nf_conncount_add take too much time,
causing several CPU lockup. This happens when user set the
conntrack limit to +20,000, because the larger the limit,
the longer the list that GC has to traverse.

The patch mitigate the performance issue by avoiding unnecessary
GC with a timestamp. Whenever nf_conncount has done a GC,
a timestamp is updated, and beforce the next time GC is
triggered, we make sure it's more than a jiffies.
By doin this we can greatly reduce the CPU cycles and
avoid the softirq lockup.

To reproduce it in OVS,
$ ovs-appctl dpctl/ct-set-limits zone=1,limit=20000
$ ovs-appctl dpctl/ct-get-limits

At another machine, runs two nmap
$ nmap -p1- <IP>
$ nmap -p1- <IP>

Signed-off-by: William Tu <u9012063@gmail.com>
Co-authored-by: Yifeng Sun <pkusunyifeng@gmail.com>
Reported-by: Greg Rose <gvrose8192@gmail.com>
Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
William Tu 2022-05-04 08:35:59 -07:00 committed by Pablo Neira Ayuso
parent 2c50fc0475
commit d265929930
2 changed files with 12 additions and 0 deletions
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1
include/net/netfilter/nf_conntrack_count.h
View file

@ -10,6 +10,7 @@ struct nf_conncount_data;
struct nf_conncount_list {
spinlock_t list_lock;
u32 last_gc; /* jiffies at most recent gc */
struct list_head head; /* connections with the same filtering key */
unsigned int count; /* length of list */
};

11
net/netfilter/nf_conncount.c
View file

@ -132,6 +132,9 @@ static int __nf_conncount_add(struct net *net,
struct nf_conn *found_ct;
unsigned int collect = 0;
if (time_is_after_eq_jiffies((unsigned long)list->last_gc))
goto add_new_node;
/* check the saved connections */
list_for_each_entry_safe(conn, conn_n, &list->head, node) {
if (collect > CONNCOUNT_GC_MAX_NODES)
@ -177,6 +180,7 @@ static int __nf_conncount_add(struct net *net,
nf_ct_put(found_ct);
}
add_new_node:
if (WARN_ON_ONCE(list->count > INT_MAX))
return -EOVERFLOW;
@ -190,6 +194,7 @@ static int __nf_conncount_add(struct net *net,
conn->jiffies32 = (u32)jiffies;
list_add_tail(&conn->node, &list->head);
list->count++;
list->last_gc = (u32)jiffies;
return 0;
}
@ -214,6 +219,7 @@ void nf_conncount_list_init(struct nf_conncount_list *list)
spin_lock_init(&list->list_lock);
INIT_LIST_HEAD(&list->head);
list->count = 0;
list->last_gc = (u32)jiffies;
}
EXPORT_SYMBOL_GPL(nf_conncount_list_init);
@ -227,6 +233,10 @@ bool nf_conncount_gc_list(struct net *net,
unsigned int collected = 0;
bool ret = false;
/* don't bother if we just did GC */
if (time_is_after_eq_jiffies((unsigned long)READ_ONCE(list->last_gc)))
return false;
/* don't bother if other cpu is already doing GC */
if (!spin_trylock(&list->list_lock))
return false;
@ -258,6 +268,7 @@ bool nf_conncount_gc_list(struct net *net,
if (!list->count)
ret = true;
list->last_gc = (u32)jiffies;
spin_unlock(&list->list_lock);
return ret;