netdev - Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

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Date:   Mon, 7 Jun 2021 16:04:47 -0600
From:   David Ahern <dsahern@...il.com>
To:     Roopa Prabhu <roopa@...dia.com>, David Ahern <dsahern@...nel.org>,
        netdev@...r.kernel.org, kuba@...nel.org, davem@...emloft.net
Cc:     Kasper Dupont <kasperd@...wv.06.feb.2021.kasperd.net>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: Re: [PATCH net] neighbour: allow NUD_NOARP entries to be forced GCed

On 6/7/21 12:53 PM, Roopa Prabhu wrote:
> 
> On 6/7/21 10:35 AM, David Ahern wrote:
>> IFF_POINTOPOINT interfaces use NUD_NOARP entries for IPv6. It's
>> possible to
>> fill up the neighbour table with enough entries that it will overflow for
>> valid connections after that.
>>
>> This behaviour is more prevalent after commit 58956317c8de ("neighbor:
>> Improve garbage collection") is applied, as it prevents removal from
>> entries that are not NUD_FAILED, unless they are more than 5s old.
>>
>> Fixes: 58956317c8de (neighbor: Improve garbage collection)
>> Reported-by: Kasper Dupont <kasperd@...wv.06.feb.2021.kasperd.net>
>> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
>> Signed-off-by: David Ahern <dsahern@...nel.org>
>> ---
>> rebased to net tree
> 
> 
> There are other use-cases  that use NUD_NOARP as static neighbour
> entries which should be exempt from forced gc.
> 
> for example when qualified by NTF_EXT_LEARNED for the E-VPN use-case.
> 
> The check in your patch below should exclude NTF_EXT_LEARNED entries.
> 
> 
> (unrelated to the neighbour code ,  but bridge driver also uses
> NUD_NOARP for static entries)
> 
> 

Maybe I misunderstand your comment: forced_gc does not apply to static
entries; those were moved to a separate list to avoid walking them.