[Bug 285967] [hyper-v] Changing hn MTU causes on freeze on Azure D4ds_v6 (and other v6) instances

From: <bugzilla-noreply_at_freebsd.org>
Date: Tue, 08 Apr 2025 20:57:36 UTC 
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=285967

            Bug ID: 285967
           Summary: [hyper-v] Changing hn MTU causes on freeze on Azure
                    D4ds_v6 (and other v6) instances
           Product: Base System
           Version: 14.2-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: evans.c@dell.com

Created a FreeBSD 14.2 Azure virtual machine using the D4ds_v6 instance type.
Azure image used was freebsd-14_2 (14_2-release-amd64-gen2-zfs) published by
thefreebsdfoundation.

When I tried to change the MTU, the command froze forever:

root@echenfreebsd:~ # ifconfig hn0 mtu 1520 up

^C^C^C^C^C^C^C

Any further ifconfig calls would also freeze forever when attempting to print
out hn0's information.

This is the output of the channel sysctl after the freeze:

# sysctl dev.hn.1.channel.12.br.tx.state
dev.hn.1.channel.12.br.tx.state: intrcnt:39 rindex:3000 windex:3064 imask:1
psndsz:0 fvalue:1 ravail:64 wavail:520128

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