mlxsw: spectrum_mr: Protect multicast table list with a lock

The multicast table list is traversed from a delayed work that
periodically updates the kernel about packets and bytes statistics from
each multicast route.

The list is currently protected by RTNL, but subsequent patches will
remove the driver's dependence on this contended lock.

In order to be able to remove dependence on RTNL in the next patch,
guard this list with a dedicated mutex.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c

 // SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
 /* Copyright (c) 2017-2018 Mellanox Technologies. All rights reserved */
 
+#include <linux/mutex.h>
 #include <linux/rhashtable.h>
 #include <net/ipv6.h>
 
@@ -12,6 +13,7 @@ struct mlxsw_sp_mr {
 	void *catchall_route_priv;
 	struct delayed_work stats_update_dw;
 	struct list_head table_list;
+	struct mutex table_list_lock; /* Protects table_list */
 #define MLXSW_SP_MR_ROUTES_COUNTER_UPDATE_INTERVAL 5000 /* ms */
 	unsigned long priv[0];
 	/* priv has to be always the last item */
@@ -926,7 +928,9 @@ struct mlxsw_sp_mr_table *mlxsw_sp_mr_table_create(struct mlxsw_sp *mlxsw_sp,
 				       &catchall_route_params);
 	if (err)
 		goto err_ops_route_create;
+	mutex_lock(&mr->table_list_lock);
 	list_add_tail(&mr_table->node, &mr->table_list);
+	mutex_unlock(&mr->table_list_lock);
 	return mr_table;
 
 err_ops_route_create:
@@ -942,7 +946,9 @@ void mlxsw_sp_mr_table_destroy(struct mlxsw_sp_mr_table *mr_table)
 	struct mlxsw_sp_mr *mr = mlxsw_sp->mr;
 
 	WARN_ON(!mlxsw_sp_mr_table_empty(mr_table));
+	mutex_lock(&mr->table_list_lock);
 	list_del(&mr_table->node);
+	mutex_unlock(&mr->table_list_lock);
 	mr->mr_ops->route_destroy(mlxsw_sp, mr->priv,
 				  &mr_table->catchall_route_priv);
 	rhashtable_destroy(&mr_table->route_ht);
@@ -1000,10 +1006,12 @@ static void mlxsw_sp_mr_stats_update(struct work_struct *work)
 	unsigned long interval;
 
 	rtnl_lock();
+	mutex_lock(&mr->table_list_lock);
 	list_for_each_entry(mr_table, &mr->table_list, node)
 		list_for_each_entry(mr_route, &mr_table->route_list, node)
 			mlxsw_sp_mr_route_stats_update(mr_table->mlxsw_sp,
 						       mr_route);
+	mutex_unlock(&mr->table_list_lock);
 	rtnl_unlock();
 
 	interval = msecs_to_jiffies(MLXSW_SP_MR_ROUTES_COUNTER_UPDATE_INTERVAL);
@@ -1023,6 +1031,7 @@ int mlxsw_sp_mr_init(struct mlxsw_sp *mlxsw_sp,
 	mr->mr_ops = mr_ops;
 	mlxsw_sp->mr = mr;
 	INIT_LIST_HEAD(&mr->table_list);
+	mutex_init(&mr->table_list_lock);
 
 	err = mr_ops->init(mlxsw_sp, mr->priv);
 	if (err)
@@ -1034,6 +1043,7 @@ int mlxsw_sp_mr_init(struct mlxsw_sp *mlxsw_sp,
 	mlxsw_core_schedule_dw(&mr->stats_update_dw, interval);
 	return 0;
 err:
+	mutex_destroy(&mr->table_list_lock);
 	kfree(mr);
 	return err;
 }
@@ -1044,5 +1054,6 @@ void mlxsw_sp_mr_fini(struct mlxsw_sp *mlxsw_sp)
 
 	cancel_delayed_work_sync(&mr->stats_update_dw);
 	mr->mr_ops->fini(mlxsw_sp, mr->priv);
+	mutex_destroy(&mr->table_list_lock);
 	kfree(mr);
 }