netdev - Re: [net-next v2] net: change accept_ra_min_rtr

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Message-ID: <ZMJh1RS+EaGsmgZJ@corigine.com>
Date: Thu, 27 Jul 2023 14:23:49 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Patrick Rohr <prohr@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Linux Network Development Mailing List <netdev@...r.kernel.org>,
	Maciej Żenczykowski <maze@...gle.com>,
	Lorenzo Colitti <lorenzo@...gle.com>,
	David Ahern <dsahern@...nel.org>
Subject: Re: [net-next v2] net: change accept_ra_min_rtr_lft to affect all RA
 lifetimes

On Wed, Jul 26, 2023 at 04:07:01PM -0700, Patrick Rohr wrote:
> accept_ra_min_rtr_lft only considered the lifetime of the default route
> and discarded entire RAs accordingly.
> 
> This change renames accept_ra_min_rtr_lft to accept_ra_min_lft, and
> applies the value to individual RA sections; in particular, router
> lifetime, PIO preferred lifetime, and RIO lifetime. If any of those
> lifetimes are lower than the configured value, the specific RA section
> is ignored.
> 
> In order for the sysctl to be useful to Android, it should really apply
> to all lifetimes in the RA, since that is what determines the minimum
> frequency at which RAs must be processed by the kernel. Android uses
> hardware offloads to drop RAs for a fraction of the minimum of all
> lifetimes present in the RA (some networks have very frequent RAs (5s)
> with high lifetimes (2h)). Despite this, we have encountered networks
> that set the router lifetime to 30s which results in very frequent CPU
> wakeups. Instead of disabling IPv6 (and dropping IPv6 ethertype in the
> WiFi firmware) entirely on such networks, it seems better to ignore the
> misconfigured routers while still processing RAs from other IPv6 routers
> on the same network (i.e. to support IoT applications).
> 
> The previous implementation dropped the entire RA based on router
> lifetime. This turned out to be hard to expand to the other lifetimes
> present in the RA in a consistent manner; dropping the entire RA based
> on RIO/PIO lifetimes would essentially require parsing the whole thing
> twice.
> 
> Fixes: 1671bcfd76fd ("net: add sysctl accept_ra_min_rtr_lft")
> Cc: Maciej Żenczykowski <maze@...gle.com>
> Cc: Lorenzo Colitti <lorenzo@...gle.com>
> Cc: David Ahern <dsahern@...nel.org>
> Signed-off-by: Patrick Rohr <prohr@...gle.com>
> ---
>  Documentation/networking/ip-sysctl.rst |  8 ++++----
>  include/linux/ipv6.h                   |  2 +-
>  include/uapi/linux/ipv6.h              |  2 +-
>  net/ipv6/addrconf.c                    | 14 ++++++++-----
>  net/ipv6/ndisc.c                       | 27 +++++++++++---------------
>  5 files changed, 26 insertions(+), 27 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 37603ad6126b..a66054d0763a 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -2288,11 +2288,11 @@ accept_ra_min_hop_limit - INTEGER
>  
>  	Default: 1
>  
> -accept_ra_min_rtr_lft - INTEGER
> -	Minimum acceptable router lifetime in Router Advertisement.
> +accept_ra_min_lft - INTEGER
> +	Minimum acceptable lifetime value in Router Advertisement.

Hi Patrick, all,

I am concerned about UAPI-breakage aspects of changing the name of a sysctl.
Can we discuss that?