netfilter: x_tables: dont block BH while reading counters

Using "iptables -L" with a lot of rules have a too big BH latency.
Jesper mentioned ~6 ms and worried of frame drops.

Switch to a per_cpu seqlock scheme, so that taking a snapshot of
counters doesnt need to block BH (for this cpu, but also other cpus).

This adds two increments on seqlock sequence per ipt_do_table() call,
its a reasonable cost for allowing "iptables -L" not block BH
processing.

Reported-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 742bec051440..6712e713b299 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -472,7 +472,7 @@ extern void xt_free_table_info(struct xt_table_info *info);
  *  necessary for reading the counters.
  */
 struct xt_info_lock {
-        spinlock_t lock;
+        seqlock_t lock;
         unsigned char readers;
 };
 DECLARE_PER_CPU(struct xt_info_lock, xt_info_locks);
@@ -497,7 +497,7 @@ static inline void xt_info_rdlock_bh(void)
         local_bh_disable();
         lock = &__get_cpu_var(xt_info_locks);
         if (likely(!lock->readers++))
-                spin_lock(&lock->lock);
+                write_seqlock(&lock->lock);
 }
 
 static inline void xt_info_rdunlock_bh(void)
@@ -505,7 +505,7 @@ static inline void xt_info_rdunlock_bh(void)
         struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);
 
         if (likely(!--lock->readers))
-                spin_unlock(&lock->lock);
+                write_sequnlock(&lock->lock);
         local_bh_enable();
 }
 
@@ -516,12 +516,12 @@ static inline void xt_info_rdunlock_bh(void)
  */
 static inline void xt_info_wrlock(unsigned int cpu)
 {
-        spin_lock(&per_cpu(xt_info_locks, cpu).lock);
+        write_seqlock(&per_cpu(xt_info_locks, cpu).lock);
 }
 
 static inline void xt_info_wrunlock(unsigned int cpu)
 {
-        spin_unlock(&per_cpu(xt_info_locks, cpu).lock);
+        write_sequnlock(&per_cpu(xt_info_locks, cpu).lock);
 }
 
 /*