net: Convert atomic_t net::count to refcount_t

Since net could be obtained from RCU lists,
and there is a race with net destruction,
the patch converts net::count to refcount_t.

This provides sanity checks for the cases of
incrementing counter of already dead net,
when maybe_get_net() has to used instead
of get_net().

Drivers: allyesconfig and allmodconfig are OK.
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/net_namespace.h

@@ -51,7 +51,7 @@ struct net {
 	refcount_t		passive;	/* To decided when the network
 						 * namespace should be freed.
 						 */
-	atomic_t		count;		/* To decided when the network
+	refcount_t		count;		/* To decided when the network
 						 *  namespace should be shut down.
 						 */
 	spinlock_t		rules_mod_lock;
@@ -195,7 +195,7 @@ void __put_net(struct net *net);
 
 static inline struct net *get_net(struct net *net)
 {
-	atomic_inc(&net->count);
+	refcount_inc(&net->count);
 	return net;
 }
 
@@ -206,14 +206,14 @@ static inline struct net *maybe_get_net(struct net *net)
 	 * exists.  If the reference count is zero this
 	 * function fails and returns NULL.
 	 */
-	if (!atomic_inc_not_zero(&net->count))
+	if (!refcount_inc_not_zero(&net->count))
 		net = NULL;
 	return net;
 }
 
 static inline void put_net(struct net *net)
 {
-	if (atomic_dec_and_test(&net->count))
+	if (refcount_dec_and_test(&net->count))
 		__put_net(net);
 }
 

net/core/net-sysfs.c

@@ -961,7 +961,7 @@ net_rx_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
 	while (--i >= new_num) {
 		struct kobject *kobj = &dev->_rx[i].kobj;
 
-		if (!atomic_read(&dev_net(dev)->count))
+		if (!refcount_read(&dev_net(dev)->count))
 			kobj->uevent_suppress = 1;
 		if (dev->sysfs_rx_queue_group)
 			sysfs_remove_group(kobj, dev->sysfs_rx_queue_group);
@@ -1367,7 +1367,7 @@ netdev_queue_update_kobjects(struct net_device *dev, int old_num, int new_num)
 	while (--i >= new_num) {
 		struct netdev_queue *queue = dev->_tx + i;
 
-		if (!atomic_read(&dev_net(dev)->count))
+		if (!refcount_read(&dev_net(dev)->count))
 			queue->kobj.uevent_suppress = 1;
 #ifdef CONFIG_BQL
 		sysfs_remove_group(&queue->kobj, &dql_group);
@@ -1558,7 +1558,7 @@ void netdev_unregister_kobject(struct net_device *ndev)
 {
 	struct device *dev = &ndev->dev;
 
-	if (!atomic_read(&dev_net(ndev)->count))
+	if (!refcount_read(&dev_net(ndev)->count))
 		dev_set_uevent_suppress(dev, 1);
 
 	kobject_get(&dev->kobj);

net/core/net_namespace.c

@@ -35,7 +35,7 @@ LIST_HEAD(net_namespace_list);
 EXPORT_SYMBOL_GPL(net_namespace_list);
 
 struct net init_net = {
-	.count		= ATOMIC_INIT(1),
+	.count		= REFCOUNT_INIT(1),
 	.dev_base_head	= LIST_HEAD_INIT(init_net.dev_base_head),
 };
 EXPORT_SYMBOL(init_net);
@@ -224,10 +224,10 @@ int peernet2id_alloc(struct net *net, struct net *peer)
 	bool alloc;
 	int id;
 
-	if (atomic_read(&net->count) == 0)
+	if (refcount_read(&net->count) == 0)
 		return NETNSA_NSID_NOT_ASSIGNED;
 	spin_lock_bh(&net->nsid_lock);
-	alloc = atomic_read(&peer->count) == 0 ? false : true;
+	alloc = refcount_read(&peer->count) == 0 ? false : true;
 	id = __peernet2id_alloc(net, peer, &alloc);
 	spin_unlock_bh(&net->nsid_lock);
 	if (alloc && id >= 0)
@@ -284,7 +284,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
 	int error = 0;
 	LIST_HEAD(net_exit_list);
 
-	atomic_set(&net->count, 1);
+	refcount_set(&net->count, 1);
 	refcount_set(&net->passive, 1);
 	net->dev_base_seq = 1;
 	net->user_ns = user_ns;

net/ipv4/inet_timewait_sock.c

@@ -270,14 +270,14 @@ void inet_twsk_purge(struct inet_hashinfo *hashinfo, int family)
 				continue;
 			tw = inet_twsk(sk);
 			if ((tw->tw_family != family) ||
-				atomic_read(&twsk_net(tw)->count))
+				refcount_read(&twsk_net(tw)->count))
 				continue;
 
 			if (unlikely(!refcount_inc_not_zero(&tw->tw_refcnt)))
 				continue;
 
 			if (unlikely((tw->tw_family != family) ||
-				     atomic_read(&twsk_net(tw)->count))) {
+				     refcount_read(&twsk_net(tw)->count))) {
 				inet_twsk_put(tw);
 				goto restart;
 			}

net/ipv4/tcp_metrics.c

@@ -892,7 +892,7 @@ static void tcp_metrics_flush_all(struct net *net)
 		pp = &hb->chain;
 		for (tm = deref_locked(*pp); tm; tm = deref_locked(*pp)) {
 			match = net ? net_eq(tm_net(tm), net) :
-				!atomic_read(&tm_net(tm)->count);
+				!refcount_read(&tm_net(tm)->count);
 			if (match) {
 				*pp = tm->tcpm_next;
 				kfree_rcu(tm, rcu_head);