net: make devnet_rename_seq a mutex

On RT write_seqcount_begin() disables preemption and device_rename()
allocates memory with GFP_KERNEL and grabs later the sysfs_mutex mutex.
Since I don't see a reason why this can't be a mutex, make it one. We
probably don't have that much reads at the same time in the hot path.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

2 files changed, 14 insertions, 17 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index b5e6b50..dce8f51 100644
--- a/net/core/dev.c
+++ b/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);
 
-seqcount_t devnet_rename_seq;
+DEFINE_MUTEX(devnet_rename_mutex);
 
 static inline void dev_base_seq_inc(struct net *net)
 {
@@ -1093,10 +1093,11 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	if (dev->flags & IFF_UP)
 		return -EBUSY;
 
-	write_seqcount_begin(&devnet_rename_seq);
+
+	mutex_lock(&devnet_rename_mutex);
 
 	if (strncmp(newname, dev->name, IFNAMSIZ) == 0) {
-		write_seqcount_end(&devnet_rename_seq);
+		mutex_unlock(&devnet_rename_mutex);
 		return 0;
 	}
 
@@ -1104,7 +1105,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
 	err = dev_get_valid_name(net, dev, newname);
 	if (err < 0) {
-		write_seqcount_end(&devnet_rename_seq);
+		mutex_unlock(&devnet_rename_mutex);
 		return err;
 	}
 
@@ -1112,11 +1113,11 @@ rollback:
 	ret = device_rename(&dev->dev, dev->name);
 	if (ret) {
 		memcpy(dev->name, oldname, IFNAMSIZ);
-		write_seqcount_end(&devnet_rename_seq);
+		mutex_unlock(&devnet_rename_mutex);
 		return ret;
 	}
 
-	write_seqcount_end(&devnet_rename_seq);
+	mutex_unlock(&devnet_rename_mutex);
 
 	write_lock_bh(&dev_base_lock);
 	hlist_del_rcu(&dev->name_hlist);
@@ -1135,7 +1136,7 @@ rollback:
 		/* err >= 0 after dev_alloc_name() or stores the first errno */
 		if (err >= 0) {
 			err = ret;
-			write_seqcount_begin(&devnet_rename_seq);
+			mutex_lock(&devnet_rename_mutex);
 			memcpy(dev->name, oldname, IFNAMSIZ);
 			goto rollback;
 		} else {
@@ -4219,7 +4220,6 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
 {
 	struct net_device *dev;
 	struct ifreq ifr;
-	unsigned seq;
 
 	/*
 	 *	Fetch the caller's info block.
@@ -4228,19 +4228,18 @@ static int dev_ifname(struct net *net, struct ifreq __user *arg)
 	if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
 		return -EFAULT;
 
-retry:
-	seq = read_seqcount_begin(&devnet_rename_seq);
+	mutex_lock(&devnet_rename_mutex);
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(net, ifr.ifr_ifindex);
 	if (!dev) {
 		rcu_read_unlock();
+		mutex_unlock(&devnet_rename_mutex);
 		return -ENODEV;
 	}
 
 	strcpy(ifr.ifr_name, dev->name);
 	rcu_read_unlock();
-	if (read_seqcount_retry(&devnet_rename_seq, seq))
-		goto retry;
+	mutex_unlock(&devnet_rename_mutex);
 
 	if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))
 		return -EFAULT;
diff --git a/net/core/sock.c b/net/core/sock.c
index 45a50ee..2754c99 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -571,7 +571,6 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
 	struct net *net = sock_net(sk);
 	struct net_device *dev;
 	char devname[IFNAMSIZ];
-	unsigned seq;
 
 	if (sk->sk_bound_dev_if == 0) {
 		len = 0;
@@ -582,20 +581,19 @@ static int sock_getbindtodevice(struct sock *sk, char __user *optval,
 	if (len < IFNAMSIZ)
 		goto out;
 
-retry:
-	seq = read_seqcount_begin(&devnet_rename_seq);
+	mutex_lock(&devnet_rename_mutex);
 	rcu_read_lock();
 	dev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
 	ret = -ENODEV;
 	if (!dev) {
 		rcu_read_unlock();
+		mutex_unlock(&devnet_rename_mutex);
 		goto out;
 	}
 
 	strcpy(devname, dev->name);
 	rcu_read_unlock();
-	if (read_seqcount_retry(&devnet_rename_seq, seq))
-		goto retry;
+	mutex_unlock(&devnet_rename_mutex);
 
 	len = strlen(devname) + 1;