IB/ipoib: Set device connection mode only when needed

commit 80b5b35a upstream.

When changing the connection mode, the ipoib_set_mode function
did not check if the previous connection mode equals to the
new one. This commit adds the required check and return 0 if the new
mode equals to the previous one.

Fixes: 839fcaba ("IPoIB: Connected mode experimental support")
Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Reviewed-by: Alex Vesker <valex@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>
[bwh: Backported to 3.2:
 - Adjust filename
 - Unlock RTNL lock before returning]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/infiniband/ulp/ipoib/ipoib_cm.c

@@ -1480,6 +1480,14 @@ static ssize_t set_mode(struct device *d, struct device_attribute *attr,
 	if (!rtnl_trylock())
 		return restart_syscall();
 
+	if ((test_bit(IPOIB_FLAG_ADMIN_CM, &priv->flags) &&
+	     !strcmp(buf, "connected\n")) ||
+	     (!test_bit(IPOIB_FLAG_ADMIN_CM, &priv->flags) &&
+	     !strcmp(buf, "datagram\n"))) {
+		rtnl_unlock();
+		return 0;
+	}
+
 	/* flush paths if we switch modes so that connections are restarted */
 	if (IPOIB_CM_SUPPORTED(dev->dev_addr) && !strcmp(buf, "connected\n")) {
 		set_bit(IPOIB_FLAG_ADMIN_CM, &priv->flags);