linux-kernel - Why do kernel panics caused by init exiting peg the CPU?

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Message-ID: <5r1aLDnOSih_aMBiFkhgpCo8RUYjlyGmTmuJ_1PB4lotjEhCdV7ROPX_HCG4WSGM63DIhm6aDJQiNAT2lD0ol7J70MCGQDfQ2PiAUNQgvDY=@protonmail.com>
Date:   Wed, 16 Jun 2021 10:22:25 +0000
From:   "Andrei E." <andreien@...tonmail.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Why do kernel panics caused by init exiting peg the CPU?

Good morning LKML,

I have noticed that using a very simple hello world program as init (very similar to the one from https://landley.net/writing/rootfs-howto.html, just with the sleep function removed) pegs the CPU on both linux (5.12.10.arch1-1) and linux-lts (5.10.43-1) kernels on Arch. Is this intended?

Steps to reproduce:
#!/bin/sh
cat << END > hello.c
#include <stdio.h>

int main(int argc, char *argv[])
{
  printf("Hello world\n");
}
END

gcc -static hello.c -o hello

mkdir sub
cp hello sub/init
cd sub
find . | cpio -o -H newc | gzip > ../initramfs_data.cpio.gz
cd ..
rm -rf sub

qemu-system-x86_64 -kernel /boot/vmlinuz-linux-lts -initrd initramfs_data.cpio.gz
# Spikes one thread to 100% usage. Causes the same issue with vmlinuz-linux.

Thank you for your time,
Andrei E.