netdev - Re: [PATCH net] ipv6: bring NLM_DONE out to a separate recv() again

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Date: Tue, 18 Jun 2024 22:40:30 +0200
From: Ilya Maximets <i.maximets@....org>
To: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc: i.maximets@....org, netdev@...r.kernel.org, edumazet@...gle.com,
 pabeni@...hat.com, Maciej Żenczykowski
 <zenczykowski@...il.com>, Stefano Brivio <sbrivio@...hat.com>,
 dsahern@...nel.org, donald.hunter@...il.com, maze@...gle.com
Subject: Re: [PATCH net] ipv6: bring NLM_DONE out to a separate recv() again

On 6/18/24 21:39, Jakub Kicinski wrote:
> Commit under Fixes optimized the number of recv() calls
> needed during RTM_GETROUTE dumps, but we got multiple
> reports of applications hanging on recv() calls.
> Applications expect that a route dump will be terminated
> with a recv() reading an individual NLM_DONE message.
> 
> Coalescing NLM_DONE is perfectly legal in netlink,
> but even tho reporters fixed the code in respective
> projects, chances are it will take time for those
> applications to get updated. So revert to old behavior
> (for now)?
> 
> This is an IPv6 version of commit 460b0d33cf10 ("inet: bring
> NLM_DONE out to a separate recv() again").
> 
> Reported-by: Maciej Żenczykowski <zenczykowski@...il.com>
> Link: https://lore.kernel.org/all/CANP3RGc1RG71oPEBXNx_WZFP9AyphJefdO4paczN92n__ds4ow@mail.gmail.com
> Reported-by: Stefano Brivio <sbrivio@...hat.com>
> Link: https://lore.kernel.org/all/20240315124808.033ff58d@elisabeth
> Reported-by: Ilya Maximets <i.maximets@....org>
> Link: https://lore.kernel.org/all/02b50aae-f0e9-47a4-8365-a977a85975d3@ovn.org
> Fixes: 5fc68320c1fb ("ipv6: remove RTNL protection from inet6_dump_fib()")
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> CC: dsahern@...nel.org
> CC: donald.hunter@...il.com
> CC: maze@...gle.com
> ---
>  net/ipv6/ip6_fib.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index d9c9a542a414..eb111d20615c 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -2514,7 +2514,8 @@ int __init fib6_init(void)
>  		goto out_kmem_cache_create;
>  
>  	ret = rtnl_register_module(THIS_MODULE, PF_INET6, RTM_GETROUTE, NULL,
> -				   inet6_dump_fib, RTNL_FLAG_DUMP_UNLOCKED);
> +				   inet6_dump_fib, RTNL_FLAG_DUMP_UNLOCKED |
> +				   RTNL_FLAG_DUMP_SPLIT_NLM_DONE);
>  	if (ret)
>  		goto out_unregister_subsys;
>  

Thanks, Jakub!  LGTM.

Libreswan in OVS tests is working fine with this change on top of 6.10-rc4.
The rest of the test suite is also working fine (except for FTP conntrack,
but that's an unrelated issue).

Tested-by: Ilya Maximets <i.maximets@....org>