net: sock_bindtodevice() RCU-ification

Avoid dev_hold()/dev_put() in sock_bindtodevice()

---
 net/core/sock.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

index 5a51512..38820ea 100644
@@ -420,14 +420,16 @@ static int sock_bindtodevice(struct sock *sk, char __user *optval, int optlen)
 	if (devname[0] == '\0') {
 		index = 0;
 	} else {
-		struct net_device *dev = dev_get_by_name(net, devname);
+		struct net_device *dev;
 
+		rcu_read_lock();
+		dev = dev_get_by_name_rcu(net, devname);
+		if (dev)
+			index = dev->ifindex;
+		rcu_read_unlock();
 		ret = -ENODEV;
 		if (!dev)
 			goto out;
-
-		index = dev->ifindex;
-		dev_put(dev);
 	}
 
 	lock_sock(sk);

From: Eric Dumazet <[email protected]>
Date: Wed, 04 Nov 2009 23:36:44 +0100

Applied to net-next-2.6, thanks.

From: David Miller <[email protected]>
Date: Thu, 05 Nov 2009 21:08:30 -0800 (PST)

Eric I had to add the following patch to cure a build warning after this, just FYI:

net: Fix build warning in sock_bindtodevice().

net/core/sock.c: In function 'sock_setsockopt':
net/core/sock.c:396: warning: 'index' may be used uninitialized in this function net/core/sock.c:396: note: 'index' was declared here

GCC can't see that all paths initialize index, so just set it to the default (0) and eliminate the specific code block that handles the null device name string.

---
 net/core/sock.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

index 38820ea..76ff58d 100644
@@ -417,9 +417,8 @@ static int sock_bindtodevice(struct sock *sk, char __user *optval, int optlen)
 	if (copy_from_user(devname, optval, optlen))
 		goto out;
 
-	if (devname[0] == '\0') {
-		index = 0;
-	} else {
+	index = 0;
+	if (devname[0] != '\0') {
 		struct net_device *dev;
 
 		rcu_read_lock();

1.6.5.2

Thanks David, which gcc version are you using ?

From: Eric Dumazet <[email protected]>
Date: Fri, 06 Nov 2009 08:08:59 +0100

I'm using "gcc-4.2.4 (Ubuntu 4.2.4-1ubuntu3)" on sparc.