netdev - Re: [PATCH v5 2/3] net: add kcov handle to skb extensions

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Message-ID: <20201121100636.26aaaf8a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 21 Nov 2020 10:06:36 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Florian Westphal <fw@...len.de>
Cc:     Ido Schimmel <idosch@...sch.org>,
        Aleksandr Nogikh <aleksandrnogikh@...il.com>,
        davem@...emloft.net, johannes@...solutions.net,
        edumazet@...gle.com, andreyknvl@...gle.com, dvyukov@...gle.com,
        elver@...gle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
        willemdebruijn.kernel@...il.com,
        Aleksandr Nogikh <nogikh@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH v5 2/3] net: add kcov handle to skb extensions

On Sat, 21 Nov 2020 17:52:27 +0100 Florian Westphal wrote:
> Ido Schimmel <idosch@...sch.org> wrote:
> > Other suggestions?  
> 
> Aleksandr, why was this made into an skb extension in the first place?
> 
> AFAIU this feature is usually always disabled at build time.
> For debug builds (test farm /debug kernel etc) its always needed.
> 
> If thats the case this u64 should be an sk_buff member, not an
> extension.

Yeah, in hindsight I should have looked at how it's used. Not a great
fit for extensions. We can go back, but...

In general I'm not very happy at how this is going. First of all just
setting the handle in a couple of allocs seems to not be enough, skbs
get cloned, reused etc. There were also build problems caused by this
patch and Aleksandr & co where nowhere to be found. Now we find out
this causes leaks, how was that not caught by the syzbot it's supposed
to serve?!

So I'm leaning towards reverting the whole thing. You can attach
kretprobes and record the information you need in BPF maps.