From d265929930e2ffafc744c0ae05fb70acd53be1ee Mon Sep 17 00:00:00 2001 From: William Tu Date: Wed, 4 May 2022 08:35:59 -0700 Subject: [PATCH] netfilter: nf_conncount: reduce unnecessary GC 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- $ nmap -p1- Signed-off-by: William Tu Co-authored-by: Yifeng Sun Reported-by: Greg Rose Suggested-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- include/net/netfilter/nf_conntrack_count.h | 1 + net/netfilter/nf_conncount.c | 11 +++++++++++ 2 files changed, 12 insertions(+) diff --git a/include/net/netfilter/nf_conntrack_count.h b/include/net/netfilter/nf_conntrack_count.h index 9645b47fa7e4..e227d997fc71 100644 --- a/include/net/netfilter/nf_conntrack_count.h +++ b/include/net/netfilter/nf_conntrack_count.h @@ -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 */ }; diff --git a/net/netfilter/nf_conncount.c b/net/netfilter/nf_conncount.c index 82f36beb2e76..5d8ed6c90b7e 100644 --- a/net/netfilter/nf_conncount.c +++ b/net/netfilter/nf_conncount.c @@ -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;