linux-kernel - Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer dereference at 000001f2

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Date:   Thu, 12 Oct 2017 10:47:25 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        LKP <lkp@...org>, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [lockdep] b09be676e0 BUG: unable to handle kernel NULL pointer
 dereference at 000001f2

On Tue, Oct 03, 2017 at 10:06:34PM +0800, Fengguang Wu wrote:

> #!/bin/bash
> 
> kernel=$1
> initrd=openwrt-trinity-i386.cgz
> 
> wget --no-clobber https://github.com/fengguang/reproduce-kernel-bug/raw/master/initrd/$initrd
> 
> kvm=(
> 	qemu-system-x86_64
> 	-enable-kvm
> 	-cpu Haswell,+smep
> 	-kernel $kernel
> 	-initrd $initrd
> 	-m 256
> 	-smp 1
> 	-device e1000,netdev=net0
> 	-netdev user,id=net0
> 	-boot order=nc
> 	-no-reboot
> 	-watchdog i6300esb
> 	-watchdog-action debug
> 	-rtc base=localtime
> 	-serial stdio
> 	-display none
> 	-monitor null
> )
> 
> append=(
> 	root=/dev/ram0
> 	hung_task_panic=1
> 	debug
> 	apic=debug
> 	sysrq_always_enabled
> 	rcupdate.rcu_cpu_stall_timeout=100
> 	net.ifnames=0
> 	printk.devkmsg=on
> 	panic=-1
> 	softlockup_panic=1
> 	nmi_watchdog=panic
> 	oops=panic
> 	load_ramdisk=2
> 	prompt_ramdisk=0
> 	drbd.minor_count=8
> 	systemd.log_level=err
> 	ignore_loglevel
> 	console=tty0
> 	earlyprintk=ttyS0,115200
> 	console=ttyS0,115200
> 	vga=normal
> 	rw
> 	drbd.minor_count=8
> )
> 
> "${kvm[@]}" -append "${append[*]}"


So I was wanting to go chase that one splat you triggered, but the above
(after s/Haswell,+smep/host/) boots right up until it wants an init:

[    0.000000] Kernel command line: root=/dev/ram0 hung_task_panic=1 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw drbd.minor_count=8

[   35.721719] Kernel panic - not syncing: No working init found.  Try passing init= option to kernel. See Linux Documentation/admin-guide/init.rst for guidance.



And it did download that initrd thingy...

$ shasum openwrt-trinity-i386.cgz
0a405d02a162defd82a5ffd556fd24e0ee2f994a  openwrt-trinity-i386.cgz


Anything else I need?