Re: [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest for session lifecycle

[Pasha Tatashin]

On Wed, Nov 19, 2025 at 4:20 PM David Matlack <dmatlack@xxxxxxxxxx> wrote:
>
> On 2025-11-15 06:34 PM, Pasha Tatashin wrote:
>
> > diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
> > new file mode 100755
> > index 000000000000..3c7c6cafbef8
> > --- /dev/null
> > +++ b/tools/testing/selftests/liveupdate/do_kexec.sh
> > @@ -0,0 +1,16 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +set -e
> > +
> > +# Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
>
> It'd be nice to use proper command line options for KERNEL and INITRAMFS
> instead of relying on environment variables.

Now that tests and do_kexec are separate, I do not think we should
complicate do_kexec.sh to support every possible environment. On most
modern distros kexec is managed via systemd, and the load and reboot
commands are going to be handled through systemd. do_kexec.sh is meant
for a very simplistic environment such as with busybox rootfs to
perform selftests.

> e.g.
>
>   ./do_kexec.sh -k <kernel> -i <initramfs>
>
> > +
> > +KERNEL="${KERNEL:-/boot/bzImage}"
> > +set -- -l -s --reuse-cmdline "$KERNEL"
>
> I've observed --reuse-cmdline causing overload of the kernel command
> line when doing repeated kexecs, since it includes the built-in command
> line (CONFIG_CMDLINE) which then also gets added by the next kernel
> during boot.

There is a problem with CONFIG_CMDLINE + KEXEC, ideally, it should be
addressed in the kernel

>
> Should we have something like this instead?
>
> diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
> index 3c7c6cafbef8..2590a870993d 100755
> --- a/tools/testing/selftests/liveupdate/do_kexec.sh
> +++ b/tools/testing/selftests/liveupdate/do_kexec.sh
> @@ -4,8 +4,16 @@ set -e
>
>  # Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
>
> +# Determine the boot command line we need to pass to the kexec kernel.  Note
> +# that the kernel will append to it its builtin command line, so make sure we
> +# subtract the builtin command to avoid accumulating kernel parameters and
> +# eventually overflowing the command line.
> +full_cmdline=$(cat /proc/cmdline)
> +builtin_cmdline=$(zcat /proc/config.gz|grep CONFIG_CMDLINE=|cut -f2 -d\")

This also implies we have /proc/config.gz or CONFIG_IKCONFIG_PROC ...

> +cmdline=${full_cmdline/$builtin_cmdline /}
> +
>  KERNEL="${KERNEL:-/boot/bzImage}"
> -set -- -l -s --reuse-cmdline "$KERNEL"
> +set -- -l -s --command-line="${cmdline}" "$KERNEL"
>
>  INITRAMFS="${INITRAMFS:-/boot/initramfs}"
>  if [ -f "$INITRAMFS" ]; then
>
> > +
> > +INITRAMFS="${INITRAMFS:-/boot/initramfs}"
> > +if [ -f "$INITRAMFS" ]; then
> > +    set -- "$@" --initrd="$INITRAMFS"
> > +fi
> > +
> > +kexec "$@"
> > +kexec -e
>
> Consider separating the kexec load into its own script, in case systems have
> their own ways of shutting down for kexec.

I think, if do_kexec.sh does not work (load + reboot), the user should
use whatever the standard way on a distro to do kexec.

>
> e.g. a kexec_load.sh script that does everything that do_kexec.sh does execpt
> the `kexec -e`. Then do_kexec.sh just calls kexec_load.sh and kexec -e.