netdev - Re: [PATCH bpf-next v6 2/8] bpf: Add fd-based tcx multi-prog infra with link support

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Message-ID: <aaed850b-0c30-ab8f-09f6-9245f1af4e46@iogearbox.net>
Date: Sat, 22 Jul 2023 01:43:39 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Petr Machata <petrm@...dia.com>
Cc: ast@...nel.org, andrii@...nel.org, martin.lau@...ux.dev,
 razor@...ckwall.org, sdf@...gle.com, john.fastabend@...il.com,
 kuba@...nel.org, dxu@...uu.xyz, joe@...ium.io, toke@...nel.org,
 davem@...emloft.net, bpf@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v6 2/8] bpf: Add fd-based tcx multi-prog infra
 with link support

On 7/21/23 4:57 PM, Petr Machata wrote:
> As of this patch (commit e420bed02507), TC qdisc installation and/or
> removal cause memory access issues in the system.
> 
> A semi-minimal reproducer is:
> 
>      bash-5.2# ip l a name v1 type veth peer name v2
>      bash-5.2# ip l s dev v1 up
>      bash-5.2# ip l s dev v2 up
>      bash-5.2# tc q a dev v1 ingress
>      bash-5.2# tc q d dev v1 ingress
>      bash-5.2# tc q a dev v1 ingress
>      bash-5.2# tc q d dev v1 ingress
> 
> It's a bit finnicky, but only a little. For me, the first two "tc q"
> operations never triggered a splat. Then it could take a few "tc q a"
> "tc q d" iterations to get it to splat. So it looks like maybe the first
> "tc q d" is the problematic bit? And then there's some likelihood of
> failing on any following "tc q" operation. The above in particular
> produced three warning splats for me (attached as decoded.txt,
> decoded2.txt and decoded3.txt). Probing further:
> 
>      bash-5.2# tc q a dev v1 ingress
> 
> Produced two more splats from KASAN (decoded4.txt and decoded5.txt),
> which look more serious.
> 
> Further attempts to prod the system deadlock it, I guess because RTNL
> was left locked.
> 
> Reverting e420bed02507, and fe20ce3a5126 + 55cc3768473e that fail to
> build without it, makes net-next/main work again.

Sorry about that, fix should be here:
https://lore.kernel.org/netdev/20230721233330.5678-1-daniel@iogearbox.net/

Thanks,
Daniel