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

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Message-ID: <aR40oVOxZ-dezpy0@google.com>
Date: Wed, 19 Nov 2025 21:20:33 +0000
From: David Matlack <dmatlack@...gle.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest
 for session lifecycle

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.

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.

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\")
+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.

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.