netdev - Re: [Patch net v7 0/9] netem: Fix skb duplication logic and prevent infinite loops

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Message-ID: <20260115183351.3ffc833e@kicinski-fedora-PF5CM1Y0>
Date: Thu, 15 Jan 2026 18:33:55 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org
Subject: Re: [Patch net v7 0/9] netem: Fix skb duplication logic and prevent
 infinite loops

On Tue, 13 Jan 2026 11:06:25 -0800 Cong Wang wrote:
> This patchset fixes the infinite loops due to duplication in netem, the
> real root cause of this problem is enqueuing to the root qdisc, which is
> now changed to enqueuing to the same qdisc. This is more reasonable,
> more intuitive from users' perspective, less error-prone and more elegant
> from kernel developers' perspective.
> 
> Please see more details in patch 4/9 which contains two pages of detailed
> explanation including why it is safe and better.
> 
> This reverts the offending commits from William which clearly broke
> mq+netem use cases, as reported by two users.
> 
> All the TC test cases pass with this patchset.

Hi Cong, looks like this was failing in TCD

# not ok 709 7c3b - Test nested DRR with NETEM duplication
# Value doesn't match: bytes: 98 != 196
# Matching against output: {'kind': 'netem', 'handle': '3:', 'parent': '2:1', 'options': {'limit': 1000, 'duplicate': {'duplicate': 1, 'correlation': 0}, 'seed': 11404757756329248505, 'ecn': False, 'gap': 0}, 'bytes': 196, 'packets': 2, 'drops': 0, 'overlimits': 0, 'requeues': 0, 'backlog': 0, 'qlen': 0}

https://github.com/p4tc-dev/tc-executor/blob/storage/artifacts/474644/1-tdc-sh/stdout

So I marked it as changes requested.