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

On 10/26/2015 09:05 AM, Hannes Frederic Sowa wrote:

Hi Alex,

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

quoted

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 te

I think I was getting a bit a head of myself.  I was looking over the 
NETDEV_UP code and thinking that we could just fall into that path since 
it is already calling ipv6_add_dev.  However now I am wondering if maybe 
we need to look at adding an idev allocation somewhere before the 
disable_ipv6 check.  I assume that is why you were allocating the idev 
before you were getting into NETDEV_UP?

quoted

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.

What I meant was that you don't need to change the event.  If you change 
the check inside the NETDEV_UP/CHANGE code path so that it tests for 
event != NETDEV_CHANGE instead of event == NETDEV_UP you don't need to 
change the event type.

Sure, I wait.

Might be a bit longer.  I just realized that I think there is another 
bug here where you are going through the NETDEV_UP path even though the 
interface isn't up.  I'll run through some testing this morning to work 
out the kinks.

- Alex