net: devnet_rename_seq should be a seqcount

Using a seqlock for devnet_rename_seq is not a good idea,
as device_rename() can sleep.

As we hold RTNL, we dont need a protection for writers,
and only need a seqcount so that readers can catch a change done
by a writer.

Bug added in commit c91f6df2 (sockopt: Change getsockopt() of
SO_BINDTODEVICE to return an interface name)
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Brian Haley <brian.haley@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1576,7 +1576,7 @@ extern int call_netdevice_notifiers(unsigned long val, struct net_device *dev);
 
 extern rwlock_t				dev_base_lock;		/* Device list lock */
 
-extern seqlock_t	devnet_rename_seq;	/* Device rename lock */
+extern seqcount_t	devnet_rename_seq;	/* Device rename seq */
 
 
 #define for_each_netdev(net, d)		\

net/core/dev.c

@@ -203,7 +203,7 @@ static struct list_head offload_base __read_mostly;
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
-DEFINE_SEQLOCK(devnet_rename_seq);
+seqcount_t devnet_rename_seq;
 
 static inline void dev_base_seq_inc(struct net *net)
 {
@@ -1093,10 +1093,10 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	if (dev->flags & IFF_UP)
 		return -EBUSY;
 
-	write_seqlock(&devnet_rename_seq);
+	write_seqcount_begin(&devnet_rename_seq);
 
 	if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
-		write_sequnlock(&devnet_rename_seq);
+		write_seqcount_end(&devnet_rename_seq);
 		return 0;
 	}
 
@@ -1104,7 +1104,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
 	err = dev_get_valid_name(net, dev, newname);
 	if (err < 0) {
-		write_sequnlock(&devnet_rename_seq);
+		write_seqcount_end(&devnet_rename_seq);
 		return err;
 	}
 
@@ -1112,11 +1112,11 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	ret = device_rename(&dev->dev, dev->name);
 	if (ret) {
 		memcpy(dev->name, oldname, IFNAMSIZ);
-		write_sequnlock(&devnet_rename_seq);
+		write_seqcount_end(&devnet_rename_seq);
 		return ret;
 	}
 
-	write_sequnlock(&devnet_rename_seq);
+	write_seqcount_end(&devnet_rename_seq);
 
 	write_lock_bh(&dev_base_lock);
 	hlist_del_rcu(&dev->name_hlist);
@@ -1135,7 +1135,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
 		/* err >= 0 after dev_alloc_name() or stores the first errno */
 		if (err >= 0) {
 			err = ret;
-			write_seqlock(&devnet_rename_seq);
+			write_seqcount_begin(&devnet_rename_seq);
 			memcpy(dev->name, oldname, IFNAMSIZ);
 			goto rollback;
 		} else {
@@ -4180,7 +4180,7 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
 		return -EFAULT;
 
 retry:
-	seq = read_seqbegin(&devnet_rename_seq);
+	seq = read_seqcount_begin(&devnet_rename_seq);
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(net, ifr.ifr_ifindex);
 	if (!dev) {
@@ -4190,7 +4190,7 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
 
 	strcpy(ifr.ifr_name, dev->name);
 	rcu_read_unlock();
-	if (read_seqretry(&devnet_rename_seq, seq))
+	if (read_seqcount_retry(&devnet_rename_seq, seq))
 		goto retry;
 
 	if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))

net/core/sock.c

@@ -583,7 +583,7 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
 		goto out;
 
 retry:
-	seq = read_seqbegin(&devnet_rename_seq);
+	seq = read_seqcount_begin(&devnet_rename_seq);
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
 	ret = -ENODEV;
@@ -594,7 +594,7 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
 
 	strcpy(devname, dev->name);
 	rcu_read_unlock();
-	if (read_seqretry(&devnet_rename_seq, seq))
+	if (read_seqcount_retry(&devnet_rename_seq, seq))
 		goto retry;
 
 	len = strlen(devname) + 1;