netfilter: revised locking for x_tables
The x_tables are organized with a table structure and a per-cpu copies
of the counters and rules. On older kernels there was a reader/writer
lock per table which was a performance bottleneck. In 2.6.30-rc, this
was converted to use RCU and the counters/rules which solved the performance
problems for do_table but made replacing rules much slower because of
the necessary RCU grace period.
This version uses a per-cpu set of spinlocks and counters to allow to
table processing to proceed without the cache thrashing of a global
reader lock and keeps the same performance for table updates.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 509a956..150e5cf 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -625,20 +625,6 @@
}
EXPORT_SYMBOL(xt_free_table_info);
-void xt_table_entry_swap_rcu(struct xt_table_info *oldinfo,
- struct xt_table_info *newinfo)
-{
- unsigned int cpu;
-
- for_each_possible_cpu(cpu) {
- void *p = oldinfo->entries[cpu];
- rcu_assign_pointer(oldinfo->entries[cpu], newinfo->entries[cpu]);
- newinfo->entries[cpu] = p;
- }
-
-}
-EXPORT_SYMBOL_GPL(xt_table_entry_swap_rcu);
-
/* Find table by name, grabs mutex & ref. Returns ERR_PTR() on error. */
struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
const char *name)
@@ -676,32 +662,43 @@
EXPORT_SYMBOL_GPL(xt_compat_unlock);
#endif
+DEFINE_PER_CPU(struct xt_info_lock, xt_info_locks);
+EXPORT_PER_CPU_SYMBOL_GPL(xt_info_locks);
+
+
struct xt_table_info *
xt_replace_table(struct xt_table *table,
unsigned int num_counters,
struct xt_table_info *newinfo,
int *error)
{
- struct xt_table_info *oldinfo, *private;
+ struct xt_table_info *private;
/* Do the substitution. */
- mutex_lock(&table->lock);
+ local_bh_disable();
private = table->private;
+
/* Check inside lock: is the old number correct? */
if (num_counters != private->number) {
duprintf("num_counters != table->private->number (%u/%u)\n",
num_counters, private->number);
- mutex_unlock(&table->lock);
+ local_bh_enable();
*error = -EAGAIN;
return NULL;
}
- oldinfo = private;
- rcu_assign_pointer(table->private, newinfo);
- newinfo->initial_entries = oldinfo->initial_entries;
- mutex_unlock(&table->lock);
- synchronize_net();
- return oldinfo;
+ table->private = newinfo;
+ newinfo->initial_entries = private->initial_entries;
+
+ /*
+ * Even though table entries have now been swapped, other CPU's
+ * may still be using the old entries. This is okay, because
+ * resynchronization happens because of the locking done
+ * during the get_counters() routine.
+ */
+ local_bh_enable();
+
+ return private;
}
EXPORT_SYMBOL_GPL(xt_replace_table);
@@ -734,7 +731,6 @@
/* Simplifies replace_table code. */
table->private = bootstrap;
- mutex_init(&table->lock);
if (!xt_replace_table(table, 0, newinfo, &ret))
goto unlock;
@@ -1147,7 +1143,14 @@
static int __init xt_init(void)
{
- int i, rv;
+ unsigned int i;
+ int rv;
+
+ for_each_possible_cpu(i) {
+ struct xt_info_lock *lock = &per_cpu(xt_info_locks, i);
+ spin_lock_init(&lock->lock);
+ lock->readers = 0;
+ }
xt = kmalloc(sizeof(struct xt_af) * NFPROTO_NUMPROTO, GFP_KERNEL);
if (!xt)
