For our point-to-point GRE tunnels, they have IN6_ADDR_GEN_MODE_NONE
when they are created then we set IN6_ADDR_GEN_MODE_EUI64 when they
come up to generate the IPv6 link local address for the interface.
Recently we found that they were no longer generating IPv6 addresses.

Also, non-point-to-point tunnels were not generating any IPv6 link
local address and instead generating an IPv6 compat address,
breaking IPv6 communication on the tunnel.

These failures were caused by commit e5dd729460ca and this patch set
aims to resolve these issues.

Thomas Winter (2):
  ip/ip6_gre: Fix changing addr gen mode not generating IPv6 link local
    address
  ip/ip6_gre: Fix non-point-to-point tunnel not generating IPv6 link
    local address

 net/ipv6/addrconf.c | 61 ++++++++++++++++++++++++---------------------
 1 file changed, 33 insertions(+), 28 deletions(-)

-- 
2.39.0

On Tue, 24 Jan 2023 16:21:01 +1300 Thomas Winter wrote:
> For our point-to-point GRE tunnels, they have IN6_ADDR_GEN_MODE_NONE
> when they are created then we set IN6_ADDR_GEN_MODE_EUI64 when they
> come up to generate the IPv6 link local address for the interface.
> Recently we found that they were no longer generating IPv6 addresses.
> 
> Also, non-point-to-point tunnels were not generating any IPv6 link
> local address and instead generating an IPv6 compat address,
> breaking IPv6 communication on the tunnel.
> 
> These failures were caused by commit e5dd729460ca and this patch set
> aims to resolve these issues.

Ah, you have the problem statement here. It needs to go into the
patches, I'm afraid. The cover letters are not as visible in-tree
and certainly don't make it to stable trees.