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>

1 files changed, 9 insertions, 10 deletions

diff --git a/net/netfilter/xt_statistic.c b/net/netfilter/xt_statistic.c
index 96e62b8fd6b1..42ecb71d445f 100644
--- 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;
 }