linux-kernel - Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to gre

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Date:   Wed, 16 Mar 2022 15:05:23 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     menglong8.dong@...il.com, rostedt@...dmis.org, mingo@...hat.com,
        xeb@...l.ru, davem@...emloft.net, yoshfuji@...ux-ipv6.org,
        imagedong@...cent.com, edumazet@...gle.com, kafai@...com,
        talalahmad@...gle.com, keescook@...omium.org, alobakin@...me,
        flyingpeng@...cent.com, mengensun@...cent.com,
        dongli.zhang@...cle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, Biao Jiang <benbjiang@...cent.com>
Subject: Re: [PATCH net-next 1/3] net: gre_demux: add skb drop reasons to
 gre_rcv()

On 3/16/22 12:57 PM, Jakub Kicinski wrote:
> On Wed, 16 Mar 2022 08:56:14 -0600 David Ahern wrote:
>>> That's certainly true. I wonder if there is a systematic way of
>>> approaching these additions that'd help us picking the points were 
>>> we add reasons less of a judgment call.  
>>
>> In my head it's split between OS housekeeping and user visible data.
>> Housekeeping side of it is more the technical failure points like skb
>> manipulations - maybe interesting to a user collecting stats about how a
>> node is performing, but more than likely not. IMHO, those are ignored
>> for now (NOT_SPECIFIED).
>>
>> The immediate big win is for packets from a network where an analysis
>> can show code location (instruction pointer), user focused reason (csum
>> failure, 'otherhost', no socket open, no socket buffer space, ...) and
>> traceable to a specific host (headers in skb data).
> 
> Maybe I'm oversimplifying but would that mean first order of business
> is to have drop codes for where we already bump MIB exception stats?

That was the original motivation and it has since spun out of control -
walking the code base and assigning unique drop reasons for every single
call to kfree_skb.