On Tue, Dec 02, 2025 at 06:39:00PM +0800, zyc zyc wrote:

Hello,

Resend my last email without HTML.

---- zyc zyc zyc199902@zohomail.cn 在 Sat, 2025-11-29 18:57:01 写到：---

...

Hello, maintainer

I would like to report what appears to be a regression in 6.12.50 kernel release related to netem. It rejects our configuration with the message: Error: netem: cannot mix duplicating netems with other netems in tree.

This breaks setups that previously worked correctly for many years.

Our team uses multiple netem qdiscs in the same HTB branch, arranged in a parallel fashion using a prio fan-out. Each branch of the prio qdisc has its own distinct netem instance with different duplication characteristics.

This is used to emulate our production conditions where a single logical path fans out into two downstream segments, for example:

two ECMP next hops with different misbehaviour characteristics, or

an HA firewall cluster where only one node is replaying frames, or

two LAG / ToR paths where one path intermittently duplicates packets.

In our environments, only a subset of flows are affected, and different downstream devices may cause different styles of duplication. This regression breaks existing automated tests, training environments, and network simulation pipelines.

I would be happy to provide our reproducer if needed.

Thank you for your time and for maintaining Linux kernel.

Can you use 'git bisect' to find the offending commit?

thanks,

greg k-h