Re: kern/58715: cpu0: softints stuck for 16 seconds

["Roy Marples via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/58715; it has been noted by GNATS.

From: Roy Marples <roy%marples.name@localhost>
To: "gnats-bugs" <gnats-bugs%NetBSD.org@localhost>
Cc: "campbell+netbsd" <campbell+netbsd%mumble.net@localhost>
Subject: Re: kern/58715: cpu0: softints stuck for 16 seconds
Date: Thu, 03 Oct 2024 15:07:06 +0100

 Some more repro data.
 
 The host has two tap(4) interfaces into qemu guest configured using virtio-net-pci which are in a bridge(4).
 The host runs ISC DHCPd which is the only DHCP server I know which allows you to configure the same IP address for two different hardware addresses.
 Configure ISC DHCPd to ensure that both virtual nics on the guest will get the same IP address in the same subnet.
 
 The NetBSD guest is configured just to start dhcpcd as a service.
 With the above kernel patch, we no longer allow interfaces we know but don't receive on to bypass DAD.
 
 Watch dhcpcd in the VM configure one but get stuck in the other in a DAD/DECLINE/DROP/DISCOVER/DAD/DECLINE loop and watch the host panic at this point.
 Takes a few seconds for dhcpcd to suddenly stop and then about 20 more for the kernel to actually panic.
 
 Roy