netfilter: flowtable: Use rw sem as flow block lock

Currently flow offload threads are synchronized by the flow block mutex.
Use rw lock instead to increase flow insertion (read) concurrency.
Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Oz Shlomo <ozsh@mellanox.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_flow_table.h

@@ -74,7 +74,7 @@ struct nf_flowtable {
 	struct delayed_work		gc_work;
 	unsigned int			flags;
 	struct flow_block		flow_block;
-	struct mutex			flow_block_lock; /* Guards flow_block */
+	struct rw_semaphore		flow_block_lock; /* Guards flow_block */
 	possible_net_t			net;
 };
 

net/netfilter/nf_flow_table_core.c

@@ -392,7 +392,7 @@ int nf_flow_table_offload_add_cb(struct nf_flowtable *flow_table,
 	struct flow_block_cb *block_cb;
 	int err = 0;
 
-	mutex_lock(&flow_table->flow_block_lock);
+	down_write(&flow_table->flow_block_lock);
 	block_cb = flow_block_cb_lookup(block, cb, cb_priv);
 	if (block_cb) {
 		err = -EEXIST;
@@ -408,7 +408,7 @@ int nf_flow_table_offload_add_cb(struct nf_flowtable *flow_table,
 	list_add_tail(&block_cb->list, &block->cb_list);
 
 unlock:
-	mutex_unlock(&flow_table->flow_block_lock);
+	up_write(&flow_table->flow_block_lock);
 	return err;
 }
 EXPORT_SYMBOL_GPL(nf_flow_table_offload_add_cb);
@@ -419,13 +419,13 @@ void nf_flow_table_offload_del_cb(struct nf_flowtable *flow_table,
 	struct flow_block *block = &flow_table->flow_block;
 	struct flow_block_cb *block_cb;
 
-	mutex_lock(&flow_table->flow_block_lock);
+	down_write(&flow_table->flow_block_lock);
 	block_cb = flow_block_cb_lookup(block, cb, cb_priv);
 	if (block_cb)
 		list_del(&block_cb->list);
 	else
 		WARN_ON(true);
-	mutex_unlock(&flow_table->flow_block_lock);
+	up_write(&flow_table->flow_block_lock);
 }
 EXPORT_SYMBOL_GPL(nf_flow_table_offload_del_cb);
 
@@ -551,7 +551,7 @@ int nf_flow_table_init(struct nf_flowtable *flowtable)
 
 	INIT_DEFERRABLE_WORK(&flowtable->gc_work, nf_flow_offload_work_gc);
 	flow_block_init(&flowtable->flow_block);
-	mutex_init(&flowtable->flow_block_lock);
+	init_rwsem(&flowtable->flow_block_lock);
 
 	err = rhashtable_init(&flowtable->rhashtable,
 			      &nf_flow_offload_rhash_params);
@@ -614,7 +614,6 @@ void nf_flow_table_free(struct nf_flowtable *flow_table)
 	nf_flow_table_iterate(flow_table, nf_flow_offload_gc_step, flow_table);
 	nf_flow_table_offload_flush(flow_table);
 	rhashtable_destroy(&flow_table->rhashtable);
-	mutex_destroy(&flow_table->flow_block_lock);
 }
 EXPORT_SYMBOL_GPL(nf_flow_table_free);
 

net/netfilter/nf_flow_table_offload.c

@@ -691,7 +691,7 @@ static int nf_flow_offload_tuple(struct nf_flowtable *flowtable,
 	if (cmd == FLOW_CLS_REPLACE)
 		cls_flow.rule = flow_rule->rule;
 
-	mutex_lock(&flowtable->flow_block_lock);
+	down_read(&flowtable->flow_block_lock);
 	list_for_each_entry(block_cb, block_cb_list, list) {
 		err = block_cb->cb(TC_SETUP_CLSFLOWER, &cls_flow,
 				   block_cb->cb_priv);
@@ -700,7 +700,7 @@ static int nf_flow_offload_tuple(struct nf_flowtable *flowtable,
 
 		i++;
 	}
-	mutex_unlock(&flowtable->flow_block_lock);
+	up_read(&flowtable->flow_block_lock);
 
 	if (cmd == FLOW_CLS_STATS)
 		memcpy(stats, &cls_flow.stats, sizeof(*stats));