Hi, I am using a application which runs in kernel as kernel module. This kernel module creates netdevice in the stack. During runtime this netdevice is made if flag UP and DOWN. When this netdevice is made UP, my kernel module need to know the ipv6 link local address learnt on this netdevice. For this my kernel module register a callback for stack notifications using register_inet6addr_notifier. In my callback I listen for NETDEV_UP and NETDEV_DOWN notifications. On NETDEV_UP notification I check the ip address received as argument of callback function. and if it is link local address I try to use this. But looks it is not usable for another 1-2 sec. I can use it successfully after 1-2 sec.
Can anybody let me know which notification, and how, I should listen from kernel module to know that link local address is now usable.

How do you know the local address isn't available?

because sendmsg call returns with "Invalid argument". And if sendmsg is retried after 1-2 sec then it works fine. I can see following content in the RFC 4862. I feel that when stack notify the link local address to application using NET_DEVUP, it is in the tentative state and so not usable.
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tentative address - an address whose uniqueness on a link is being verified, prior to its assignment to an interface. A tentative address is not considered assigned to an interface in the usual sense. An interface discards received packets addressed to a tentative address, but accepts Neighbor Discovery packets related to Duplicate Address Detection for the tentative address
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An address is considered unique if none of the tests indicate the presence of a duplicate address within RetransTimer milliseconds after having sent DupAddrDetectTransmits Neighbor Solicitations. Once an address is determined to be unique, it may be assigned to an interface.
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You can try NETDEV_CHANGE notification to check weather the device is ready.

Will NETDEV_CHANGE be received only for link local address ready? Or it is received for some other link changes also? How to know that it is received for link local address ready?

If the device is ready, link local address should be ready, too.

So I understand that NETDEV_CHANGE will only be received indicating device ready. No other indication?

I tested and found that when I do the netdev up then NETDEV_CHANGE is not received in the callback. This callback I registered with kernel using register_inet6addr_notifier. Although NETDEV_UP (for dev up) and NETDEV_DOWN (for dev down) are received.

You can register other notifier.

Can you suggest which notifier I should use?

register_netdevice_notifier