netfilter: xt_statistic: remove nth_lock spinlock

Use atomic_cmpxchg() to avoid dirtying a shared location.

xt_statistic_priv smp aligned to avoid sharing same cache line with
other stuff.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

diff --git a/net/netfilter/xt_statistic.c b/net/netfilter/xt_statistic.c
index 96e62b8fd6b10d063f7bdc4cc2ee0ba28ed9991a..42ecb71d445fe6d009ac252d1b030cd86befcfb1 100644 (file)
--- a/net/netfilter/xt_statistic.c
+++ b/net/netfilter/xt_statistic.c
@@ -18,8 +18,8 @@
 #include <linux/netfilter/x_tables.h>
 
 struct xt_statistic_priv {
-       uint32_t count;
-};
+       atomic_t count;
+} ____cacheline_aligned_in_smp;
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
@@ -27,13 +27,12 @@ MODULE_DESCRIPTION("Xtables: statistics-based matching (\"Nth\", random)");
 MODULE_ALIAS("ipt_statistic");
 MODULE_ALIAS("ip6t_statistic");
 
-static DEFINE_SPINLOCK(nth_lock);
-
 static bool
 statistic_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
        const struct xt_statistic_info *info = par->matchinfo;
        bool ret = info->flags & XT_STATISTIC_INVERT;
+       int nval, oval;
 
        switch (info->mode) {
        case XT_STATISTIC_MODE_RANDOM:
@@ -41,12 +40,12 @@ statistic_mt(const struct sk_buff *skb, struct xt_action_param *par)
                        ret = !ret;
                break;
        case XT_STATISTIC_MODE_NTH:
-               spin_lock_bh(&nth_lock);
-               if (info->master->count++ == info->u.nth.every) {
-                       info->master->count = 0;
+               do {
+                       oval = atomic_read(&info->master->count);
+                       nval = (oval == info->u.nth.every) ? 0 : oval + 1;
+               } while (atomic_cmpxchg(&info->master->count, oval, nval) != oval);
+               if (nval == 0)
                        ret = !ret;
-               }
-               spin_unlock_bh(&nth_lock);
                break;
        }
 
@@ -64,7 +63,7 @@ static int statistic_mt_check(const struct xt_mtchk_param *par)
        info->master = kzalloc(sizeof(*info->master), GFP_KERNEL);
        if (info->master == NULL)
                return -ENOMEM;
-       info->master->count = info->u.nth.count;
+       atomic_set(&info->master->count, info->u.nth.count);
 
        return 0;
 }