netdevsim: fib: Introduce a lock to guard nexthop hashtable

Currently netdevsim relies on RTNL to maintain exclusivity in accessing the
nexthop hash table. However, bucket notification may be called without RTNL
having been held. Instead, introduce a custom lock to guard the table.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/netdevsim/fib.c

@@ -47,13 +47,14 @@ struct nsim_fib_data {
 	struct nsim_fib_entry nexthops;
 	struct rhashtable fib_rt_ht;
 	struct list_head fib_rt_list;
-	struct mutex fib_lock; /* Protects hashtable and list */
+	struct mutex fib_lock; /* Protects FIB HT and list */
 	struct notifier_block nexthop_nb;
 	struct rhashtable nexthop_ht;
 	struct devlink *devlink;
 	struct work_struct fib_event_work;
 	struct list_head fib_event_queue;
 	spinlock_t fib_event_queue_lock; /* Protects fib event queue list */
+	struct mutex nh_lock; /* Protects NH HT */
 	struct dentry *ddir;
 	bool fail_route_offload;
 };
@@ -1262,8 +1263,7 @@ static int nsim_nexthop_event_nb(struct notifier_block *nb, unsigned long event,
 	struct nh_notifier_info *info = ptr;
 	int err = 0;
 
-	ASSERT_RTNL();
-
+	mutex_lock(&data->nh_lock);
 	switch (event) {
 	case NEXTHOP_EVENT_REPLACE:
 		err = nsim_nexthop_insert(data, info);
@@ -1275,6 +1275,7 @@ static int nsim_nexthop_event_nb(struct notifier_block *nb, unsigned long event,
 		break;
 	}
 
+	mutex_unlock(&data->nh_lock);
 	return notifier_from_errno(err);
 }
 
@@ -1404,6 +1405,7 @@ struct nsim_fib_data *nsim_fib_create(struct devlink *devlink,
 	if (err)
 		goto err_data_free;
 
+	mutex_init(&data->nh_lock);
 	err = rhashtable_init(&data->nexthop_ht, &nsim_nexthop_ht_params);
 	if (err)
 		goto err_debugfs_exit;
@@ -1469,6 +1471,7 @@ struct nsim_fib_data *nsim_fib_create(struct devlink *devlink,
 				    data);
 	mutex_destroy(&data->fib_lock);
 err_debugfs_exit:
+	mutex_destroy(&data->nh_lock);
 	nsim_fib_debugfs_exit(data);
 err_data_free:
 	kfree(data);
@@ -1497,6 +1500,7 @@ void nsim_fib_destroy(struct devlink *devlink, struct nsim_fib_data *data)
 	WARN_ON_ONCE(!list_empty(&data->fib_event_queue));
 	WARN_ON_ONCE(!list_empty(&data->fib_rt_list));
 	mutex_destroy(&data->fib_lock);
+	mutex_destroy(&data->nh_lock);
 	nsim_fib_debugfs_exit(data);
 	kfree(data);
 }