Bug#1130974: linux-image-rt-amd64: -rt kernel builds are missing xt_MASQUERADE module

From	Ben Hutchings <ben@decadent.org.uk>
Newsgroups	linux.debian.bugs.dist, linux.debian.kernel
Subject	Bug#1130974: linux-image-rt-amd64: -rt kernel builds are missing xt_MASQUERADE module
Date	2026-03-16 22:40 +0100
Message-ID	<MznPj-8342-9@gated-at.bofh.it> (permalink)
References	<Mzk53-80wr-5@gated-at.bofh.it> <Mzk53-80wr-3@gated-at.bofh.it> <MznPk-8342-27@gated-at.bofh.it> <Mzk53-80wr-5@gated-at.bofh.it> <MznPk-8342-27@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Control: reassign -1 src:libvirt
Control: retitle -1 libvirt: Should use nftables for IP masquerading to work with PREEMPT_RT
Control: severity -1 minor

On Mon, 2026-03-16 at 22:04 +0100, Mariusz Gronczewski wrote:
> On Mon, 16 Mar 2026 at 18:37, Ben Hutchings <ben@decadent.org.uk> wrote:
> > 
> > Control: tag -1 upstream wontfix
> > 
> > On Mon, 2026-03-16 at 17:20 +0100, Mariusz Gronczewski wrote:
> > > Package: linux-image-rt-amd64
> > > Version: 6.19.6-2
> > > Severity: important
> > > X-Debbugs-Cc: debian-amd64@lists.debian.org
> > > User: debian-amd64@lists.debian.org
> > > Usertags: amd64
> > > 
> > > -rt packages seem to be missing this module
> > > 
> > > /lib/modules/6.18.15+deb14-amd64/kernel/net/netfilter/nft_masq.ko.xz
> > > /lib/modules/6.18.15+deb14-amd64/kernel/net/netfilter/xt_MASQUERADE.ko.xz
> > > /lib/modules/6.18.15+deb14-rt-amd64/kernel/net/netfilter/nft_masq.ko.xz
> > > /lib/modules/6.19.6+deb14+1-amd64/kernel/net/netfilter/nft_masq.ko.xz
> > > /lib/modules/6.19.6+deb14+1-amd64/kernel/net/netfilter/xt_MASQUERADE.ko.xz
> > > /lib/modules/6.19.6+deb14+1-rt-amd64/kernel/net/netfilter/nft_masq.ko.xz
> > > 
> > > while it's present in non-rt builds
> > > 
> > > That causes libvirt's default network (which uses this module and iptables for
> > > NATing) to not start
> > [...]
> > 
> > This is intentionally disabled upstream because xtables isn't compatible
> > with PREEMPT_RT.
> 
> Oh, I didn't know, I used it since 6.12 and just noticed that in newer
> ones it's unavailable and it breaks default libvirt network
> 
> Should I report it to libvirt package ? With current setup of both,
> switching to RT without changing libvirt config will just make default
> network stop working

I'm reassigning this to libvirt.  No need to open another report.

Ben.

-- 
Ben Hutchings
Anthony's Law of Force: Don't force it, get a larger hammer.

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Bug#1130974: linux-image-rt-amd64: -rt kernel builds are missing xt_MASQUERADE module Ben Hutchings <ben@decadent.org.uk> - 2026-03-16 18:40 +0100
  Processed: Re: Bug#1130974: linux-image-rt-amd64: -rt kernel  builds are missing xt_MASQUERADE module "Debian Bug Tracking System" <owner@bugs.debian.org> - 2026-03-16 18:40 +0100
  Bug#1130974: linux-image-rt-amd64: -rt kernel builds are missing xt_MASQUERADE module Ben Hutchings <ben@decadent.org.uk> - 2026-03-16 22:40 +0100

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