linux-kernel - Re: [PATCH net-next v2] ipv6: preserve insertion order for same-scope addresses

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Message-ID: <333ab7ce-55f4-4f19-a1a9-b3c86621e892@gmail.com>
Date: Mon, 5 Jan 2026 22:56:40 +0100
From: Justin Iurman <justin.iurman@...il.com>
To: Yumei Huang <yuhuang@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: sbrivio@...hat.com, david@...son.dropbear.id.au, davem@...emloft.net,
 dsahern@...nel.org, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 horms@...nel.org, shuah@...nel.org
Subject: Re: [PATCH net-next v2] ipv6: preserve insertion order for same-scope
 addresses

On 1/4/26 04:23, Yumei Huang wrote:
> IPv6 addresses with the same scope are returned in reverse insertion
> order, unlike IPv4. For example, when adding a -> b -> c, the list is
> reported as c -> b -> a, while IPv4 preserves the original order.
> 
> This behavior causes:
> 
> a. When using `ip -6 a save` and `ip -6 a restore`, addresses are restored
>     in the opposite order from which they were saved. See example below
>     showing addresses added as 1::1, 1::2, 1::3 but displayed and saved
>     in reverse order.
> 
>     # ip -6 a a 1::1 dev x
>     # ip -6 a a 1::2 dev x
>     # ip -6 a a 1::3 dev x
>     # ip -6 a s dev x
>     2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
>         inet6 1::3/128 scope global tentative
>         valid_lft forever preferred_lft forever
>         inet6 1::2/128 scope global tentative
>         valid_lft forever preferred_lft forever
>         inet6 1::1/128 scope global tentative
>         valid_lft forever preferred_lft forever
>     # ip -6 a save > dump
>     # ip -6 a d 1::1 dev x
>     # ip -6 a d 1::2 dev x
>     # ip -6 a d 1::3 dev x
>     # ip a d ::1 dev lo
>     # ip a restore < dump
>     # ip -6 a s dev x
>     2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
>         inet6 1::1/128 scope global tentative
>         valid_lft forever preferred_lft forever
>         inet6 1::2/128 scope global tentative
>         valid_lft forever preferred_lft forever
>         inet6 1::3/128 scope global tentative
>         valid_lft forever preferred_lft forever
>     # ip a showdump < dump
>      if1:
>          inet6 ::1/128 scope host proto kernel_lo
>          valid_lft forever preferred_lft forever
>      if2:
>          inet6 1::3/128 scope global tentative
>          valid_lft forever preferred_lft forever
>      if2:
>          inet6 1::2/128 scope global tentative
>          valid_lft forever preferred_lft forever
>      if2:
>          inet6 1::1/128 scope global tentative
>          valid_lft forever preferred_lft forever
> 
> b. Addresses in pasta to appear in reversed order compared to host
>     addresses.
> 
> The ipv6 addresses were added in reverse order by commit e55ffac60117
> ("[IPV6]: order addresses by scope"), then it was changed by commit
> 502a2ffd7376 ("ipv6: convert idev_list to list macros"), and restored by
> commit b54c9b98bbfb ("ipv6: Preserve pervious behavior in
> ipv6_link_dev_addr()."). However, this reverse ordering within the same
> scope causes inconsistency with IPv4 and the issues described above.
> 
> This patch aligns IPv6 address ordering with IPv4 for consistency
> by changing the comparison from >= to > when inserting addresses
> into the address list. Also updates the ioam6 selftest to reflect
> the new address ordering behavior. Combine these two changes into
> one patch for bisectability.
> 
> Fixes: e55ffac60117 ("[IPV6]: order addresses by scope")
> Link: https://bugs.passt.top/show_bug.cgi?id=175
> Suggested-by: Stefano Brivio <sbrivio@...hat.com>
> Signed-off-by: Yumei Huang <yuhuang@...hat.com>
> ---
>   net/ipv6/addrconf.c                  | 2 +-
>   tools/testing/selftests/net/ioam6.sh | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 40e9c336f6c5..ca998bf46863 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1013,7 +1013,7 @@ ipv6_link_dev_addr(struct inet6_dev *idev, struct inet6_ifaddr *ifp)
>   	list_for_each(p, &idev->addr_list) {
>   		struct inet6_ifaddr *ifa
>   			= list_entry(p, struct inet6_ifaddr, if_list);
> -		if (ifp_scope >= ipv6_addr_src_scope(&ifa->addr))
> +		if (ifp_scope > ipv6_addr_src_scope(&ifa->addr))
>   			break;
>   	}
>   
> diff --git a/tools/testing/selftests/net/ioam6.sh b/tools/testing/selftests/net/ioam6.sh
> index 845c26dd01a9..b2b99889942f 100755
> --- a/tools/testing/selftests/net/ioam6.sh
> +++ b/tools/testing/selftests/net/ioam6.sh
> @@ -273,8 +273,8 @@ setup()
>     ip -netns $ioam_node_beta link set ioam-veth-betaR name veth1 &>/dev/null
>     ip -netns $ioam_node_gamma link set ioam-veth-gamma name veth0 &>/dev/null
>   
> -  ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
>     ip -netns $ioam_node_alpha addr add 2001:db8:1::2/64 dev veth0 &>/dev/null
> +  ip -netns $ioam_node_alpha addr add 2001:db8:1::50/64 dev veth0 &>/dev/null
>     ip -netns $ioam_node_alpha link set veth0 up &>/dev/null
>     ip -netns $ioam_node_alpha link set lo up &>/dev/null
>     ip -netns $ioam_node_alpha route add 2001:db8:2::/64 \

For tools/testing/selftests/net/ioam6.sh:

Acked-by: Justin Iurman <justin.iurman@...il.com>