@@ -8,16 +8,14 @@
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/skbuff.h>
-#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_limit.h>
struct xt_limit_priv {
- spinlock_t lock;
unsigned long prev;
- uint32_t credit;
+ u32 credit;
};
MODULE_LICENSE("GPL");
@@ -66,22 +64,31 @@ limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
const struct xt_rateinfo *r = par->matchinfo;
struct xt_limit_priv *priv = r->master;
- unsigned long now = jiffies;
-
- spin_lock_bh(&priv->lock);
- priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
- if (priv->credit > r->credit_cap)
- priv->credit = r->credit_cap;
-
- if (priv->credit >= r->cost) {
- /* We're not limited. */
- priv->credit -= r->cost;
- spin_unlock_bh(&priv->lock);
- return true;
- }
-
- spin_unlock_bh(&priv->lock);
- return false;
+ unsigned long now;
+ u32 old_credit, new_credit, credit_increase = 0;
+ bool ret;
+
+ /* fastpath if there is nothing to update */
+ if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies))
+ return false;
+
+ do {
+ now = jiffies;
+ credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
+ old_credit = READ_ONCE(priv->credit);
+ new_credit = old_credit;
+ new_credit += credit_increase;
+ if (new_credit > r->credit_cap)
+ new_credit = r->credit_cap;
+ if (new_credit >= r->cost) {
+ ret = true;
+ new_credit -= r->cost;
+ } else {
+ ret = false;
+ }
+ } while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit);
+
+ return ret;
}
/* Precision saver. */
@@ -122,7 +129,6 @@ static int limit_mt_check(const struct xt_mtchk_param *par)
r->credit_cap = priv->credit; /* Credits full. */
r->cost = user2credits(r->avg);
}
- spin_lock_init(&priv->lock);
return 0;
}
We've seen this spin_lock show up high in profiles. Let's introduce a lockless version. I've tested this using pktgen_sample01_simple.sh. Signed-off-by: Jason Baron <jbaron@akamai.com> --- net/netfilter/xt_limit.c | 46 ++++++++++++++++++++++++++-------------------- 1 file changed, 26 insertions(+), 20 deletions(-)