Re: [PATCH net-next] ipv6: recreate ipv6 link-local addresses when increasing MTU over IPV6_MIN_MTU

Hi Alex,

On Mon, Oct 26, 2015, at 16:52, Alexander Duyck wrote:

On 10/26/2015 07:36 AM, Hannes Frederic Sowa wrote:

quoted

Take into consideration that the interface might be disabled for IPv6,
thus switch event type.

Signed-off-by: Hannes Frederic Sowa <redacted>
---
  net/ipv6/addrconf.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index d0c685c..c2dcebe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -3149,6 +3149,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
  
  	case NETDEV_UP:
  	case NETDEV_CHANGE:
+netdev_change:
  		if (dev->flags & IFF_SLAVE)
  			break;
  

@@ -3244,8 +3245,10 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
  
  		if (!idev && dev->mtu >= IPV6_MIN_MTU) {
  			idev = ipv6_add_dev(dev);
-			if (!IS_ERR(idev))
-				break;
+			if (!IS_ERR(idev)) {
+				event = NETDEV_UP;
+				goto netdev_change;
+			}
  		}
  
  		/*

Seems like this code isn't quite correct.  You are calling ipv6_add_dev 
for slave devices, and if I understand things correctly I don't believe 
that was happening before and may be an unintended side effect.

Hmm, could you quickly help me where I get into this situation? I made
sure I enter the NETDEV_UP part before the IFF_SLAVE test and
disable_ipv6 test.

You might want to instead just make it so that you only do the jump, and 
perhaps change the code in the NETDEV_UP/NETDEV_CHANGE section so that 
you test for NETDEV_CHANGE instead of NETDEV_UP.  That should be enough 
to get the effect you are looking for and I believe there would be no 
change to behaviour other than adding IPv6 link-local addresses when the 
MTU is increased.

Give me a bit and I can submit an alternative that may actually work out 
a bit better I think.

If you go the NETDEV_CHANGE route instead of NETDEV_UP, you end up with
the IF_READY flag already set from ipv6_add_dev and thus won't do any
initialization of the device.

Sure, I wait.

Bye,
Hannes