Re: [linux-next:master] [fs] 313c47f4fe: BUG:kernel_hang_in_test_stage

[Christian Brauner <brauner@kernel.org>]

On Tue, Jan 27, 2026 at 02:26:09PM +0800, kernel test robot wrote:
> 
> 
> Hello,
> 
> kernel test robot noticed "BUG:kernel_hang_in_test_stage" on:
> 
> commit: 313c47f4fe4d07eb2969f429a66ad331fe2b3b6f ("fs: use nullfs unconditionally as the real rootfs")
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> 
> [test failed on linux-next/master ca3a02fda4da8e2c1cb6baee5d72352e9e2cfaea]
> 
> in testcase: trinity
> version: 
> with following parameters:
> 
> 	runtime: 300s
> 	group: group-00
> 	nr_groups: 5
> 
> 
> 
> config: x86_64-kexec
> compiler: clang-20
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 32G
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)

The reproducer doesn't work:

ubuntu@pengar:~/data/kernel/linux/MODULES/lkp-tests$ sudo bin/lkp qemu -k ../../vmlinux -m ./modules.cgz job-script # job-script
result_root: /home/ubuntu/.lkp//result/trinity/group-00-5-300s/vm-snb/yocto-x86_64-minimal-20190520.cgz/x86_64-kexec/clang-20/313c47f4fe4d07eb2969f429a66ad331fe2b3b6f/15
downloading initrds ...
skip downloading /home/ubuntu/.lkp/cache/osimage/yocto/yocto-x86_64-minimal-20190520.cgz
19270 blocks
/usr/bin/wget -q --timeout=3600 --tries=1 --local-encoding=UTF-8 https://download.01.org/0day-ci/lkp-qemu/osimage/pkg/debian-x86_64-20180403.cgz/trinity-static-x86_64-x86_64-1c734c75-1_2020-01-06.cgz -N -P /home/ubuntu/.lkp/cache/osimage/pkg/debian-x86_64-20180403.cgz
Failed to download osimage/pkg/debian-x86_64-20180403.cgz/trinity-static-x86_64-x86_64-1c734c75-1_2020-01-06.cgz
cat: '': No such file or directory
exec command: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -fsdev local,id=test_dev,path=/home/ubuntu/.lkp//result/trinity/group-00-5-300s/vm-snb/yocto-x86_64-minimal-20190520.cgz/x86_64-kexec/clang-20/313c47f4fe4d07eb2969f429a66ad331fe2b3b6f/15,security_model=none -device virtio-9p-pci,fsdev=test_dev,mount_tag=9p/virtfs_mount -kernel ../../vmlinux -append root=/dev/ram0 RESULT_ROOT=/result/trinity/group-00-5-300s/vm-snb/yocto-x86_64-minimal-20190520.cgz/x86_64-kexec/clang-20/313c47f4fe4d07eb2969f429a66ad331fe2b3b6f/0 BOOT_IMAGE=/pkg/linux/x86_64-kexec/clang-20/313c47f4fe4d07eb2969f429a66ad331fe2b3b6f/vmlinuz-6.19.0-rc1-00006-g313c47f4fe4d branch=internal-devel/devel-hourly-20260124-050739 job=/lkp/jobs/scheduled/vm-meta-17/trinity-group-00-5-300s-yocto-x86_64-minimal-20190520.cgz-313c47f4fe4d-20260126-53110-19zhjsh-2.yaml user=lkp ARCH=x86_64 kconfig=x86_64-kexec commit=313c47f4fe4d07eb2969f429a66ad331fe2b3b6f intremap=posted_msi watchdog_thresh=240 rcuperf.shutdown=0 rcuscale.shutdown=0 refscale.shutdown=0 audit=0 kunit.enable=0 ia32_emulation=on max_uptime=7200 LKP_LOCAL_RUN=1 selinux=0 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  ip=dhcp result_service=9p/virtfs_mount -initrd /home/ubuntu/.lkp/cache/final_initrd -smp 2 -m 12872M -no-reboot -device i6300esb -rtc base=localtime -device e1000,netdev=net0 -netdev user,id=net0 -display none -monitor null -serial stdio
qemu-system-x86_64: Error loading uncompressed kernel without PVH ELF Note

The paths for the downloads in the job script are wrong or don't work.
Even if I manually modify the above path I still get in the next step:

/usr/bin/wget -q --timeout=3600 --tries=1 --local-encoding=UTF-8 https://download.01.org/0day-ci/lkp-qemu/modules.cgz -N -P /home/ubuntu/.lkp/cache
Failed to download modules.cgz
cat: '': No such file or directory

I need a way to reproduce the issue to figure out exactly what is
happening.

> 
> 
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@intel.com>
> | Closes: https://lore.kernel.org/oe-lkp/202601270735.29b7c33e-lkp@intel.com
> 
> 
> 
> [   27.746952][ T1793] /lkp/lkp/src/monitors/meminfo: line 25: /lkp/lkp/src/bin/event/wait: not found
> [   31.757224][ T1793] /lkp/lkp/src/monitors/oom-killer: line 94: dmesg: not found
> [   31.757224][ T1793] /lkp/lkp/src/monitors/oom-killer: line 94: grep: not found
> [   31.757224][ T1793] /lkp/lkp/src/monitors/oom-killer: line 25: /lkp/lkp/src/bin/event/wait: not found
> [   65.744824][ T4974] trinity-main[4974]: segfault at 0 ip 0000000000000000 sp 00007ffe08d2ec08 error 15 likely on CPU 0 (core 0, socket 0)
> [   65.746308][ T4974] Code: Unable to access opcode bytes at 0xffffffffffffffd6.
> 
> Code starting with the faulting instruction
> ===========================================
> /etc/rc5.d/S77lkp-bootstrap: line 79: sleep: not found
> BUG: kernel hang in test stage
> 
> 
> 
> The kernel config and materials to reproduce are available at:
> https://download.01.org/0day-ci/archive/20260127/202601270735.29b7c33e-lkp@intel.com
> 
> 
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
>