Re: [PATCH v9 1/9] kho: make debugfs interface optional

["Yanjun.Zhu" <yanjun.zhu@linux.dev>]

On 11/11/25 7:26 AM, Pasha Tatashin wrote:
> On Mon, Nov 10, 2025 at 11:11 PM Zhu Yanjun <yanjun.zhu@linux.dev> wrote:
>> In FC42, when I run "./luo_multi_session"
>>
>> # ./luo_multi_session
>> # [STAGE 1] Starting pre-kexec setup for multi-session test...
>> # [STAGE 1] Creating state file for next stage (2)...
>> # [STAGE 1] Creating empty sessions 'multi-test-empty-1' and
>> 'multi-test-empty-2'...
>> # [STAGE 1] Creating session 'multi-test-files-1' with one memfd...
>> # [STAGE 1] Creating session 'multi-test-files-2' with two memfds...
>> # [STAGE 1] Executing kexec...
>>
>> Then the system hang. And via virt-viewer, a calltrace will appear.
> Looks like mountroot fails, are you passing the same kernel parameters
> as the during cold boot?
> i.e. kexec -l -s --reuse-cmdline --initrd=[initramfs] [kernel]
>
> Pasha

Hi, Pasha

Following your advice, the following can work well.

I am not sure if we can merge this commit into selftests/liveupdate 
mainline?

commit 44764c48a658987b7729c5bc2be9fd87832cfbdf (HEAD -> linux-next/master)
Author: Zhu Yanjun <yanjun.zhu@linux.dev>
Date:   Thu Nov 13 11:45:21 2025 -0800

     selftests/liveupdate: Fix the error "Unable to mount root fs on 
unknown-block"

     If the initrd is not provide, the followings will appear.
     "
     Call Trace:
     <TASK>
     dump_stack_lvl+0x5d/0x80
     vpanic+0x118/8x320
     panic+0x6b/0x6b
     ? do_mount_root+0x115/0x130
      mount_root_generic+0x1cf/0x270
      prepare_namespace+0x1e1/0x230
      kernel_init_freeable+0x136/8x140
     ?_pfx_kernel_init+0x10/0x10
      kernel_init+0x1a/0x140
      ret_from_fork+0x130/0x1a8
      ?_pfx_kernel_init+0x10/0x10
      ret_from_fork_asm+0x1a/0x30
      </ TASK>
      Kernel Offset: 0x3000000 from Oxffffffff81000000
     "

     Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>

diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh 
b/tools/testing/selftests/liveupdate/do_kexec.sh
index bb396a92c3b8..4ee59abd0dd4 100755
--- a/tools/testing/selftests/liveupdate/do_kexec.sh
+++ b/tools/testing/selftests/liveupdate/do_kexec.sh
@@ -2,5 +2,5 @@
  # SPDX-License-Identifier: GPL-2.0
  set -e

-kexec -l -s --reuse-cmdline /boot/bzImage
+kexec -l -s --reuse-cmdline /boot/bzImage --initrd 
/boot/initramfs-`uname -r`.img
  kexec -e

Thanks a lot.

Yanjun.Zhu

>> The call trace is in the attachment.
>>
>> Yanjun.Zhu
>>
>> 在 2025/11/10 7:26, Pasha Tatashin 写道:
>>> On Mon, Nov 10, 2025 at 8:16 AM Pratyush Yadav <pratyush@kernel.org> wrote:
>>>> On Sun, Nov 09 2025, Zhu Yanjun wrote:
>>>>
>>>>> 在 2025/11/8 10:13, Pasha Tatashin 写道:
>>>>>> On Fri, Nov 7, 2025 at 6:36 PM Yanjun.Zhu <yanjun.zhu@linux.dev> wrote:
>>>>>>> On 11/7/25 4:02 AM, Pasha Tatashin wrote:
>>>>>>>> On Fri, Nov 7, 2025 at 7:00 AM Pasha Tatashin <pasha.tatashin@soleen.com> wrote:
>>>>>>>>>> Hi, Pasha
>>>>>>>>>>
>>>>>>>>>> In our previous discussion, we talked about counting the number of times
>>>>>>>>>> the kernel is rebooted via kexec. At that time, you suggested adding a
>>>>>>>>>> variable in debugfs to keep track of this count.
>>>>>>>>>> However, since debugfs is now optional, where would be an appropriate
>>>>>>>>>> place to store this variable?
>>>>>>>>> It is an optional config and can still be enabled if the live update
>>>>>>>>> reboot number value needs to be accessed through debugfs. However,
>>>>>>>>> given that debugfs does not guarantee a stable interface, tooling
>>>>>>>>> should not be built to require these interfaces.
>>>>>>>>>
>>>>>>>>> In the WIP LUO [1] I have, I pr_info() the live update number during
>>>>>>>>> boot and also store it in the incoming LUO FDT tree, which can also be
>>>>>>>>> accessed through this optional debugfs interface.
>>>>>>>>>
>>>>>>>>> The pr_info message appears like this during boot:
>>>>>>>>> [    0.000000] luo: Retrieved live update data, liveupdate number: 17
>>>>>>>>>
>>>>>>>>> Pasha
>>>>>>>> Forgot to add link to WIP LUOv5:
>>>>>>>> [1] https://github.com/soleen/linux/tree/luo/v5rc04
>>>>>>> Thanks a lot. I’ve carefully read this commit:
>>>>>>> https://github.com/soleen/linux/commit/60205b9a95c319dc9965f119303a1d83f0ff08fa.
>>>>>>>
>>>>>>> To be honest, I’d like to run some tests with who/luo, including the
>>>>>>> selftest for kho/luo. Could you please share the steps with me?
>>>>>>>
>>>>>>> If the testing steps have already been documented somewhere, could you
>>>>>>> please share the link?
>>>>>> Currently the test performs in-kernel tests for FLB data, it creates a
>>>>>> number of FLB for every registered LUO file-handler, which at the
>>>>>> moment is only memfd.
>>>>>>
>>>>>> It works together with any of the kexec based live update tests. In
>>>>>> v5, I introduce two tests:
>>>>>> luo_kexec_simple
>>>>>> luo_multi_session
>>>>>>
>>>>>> For example, with luo_multi_session:
>>>>> Hi, Pasha
>>>>>
>>>>> I enabled "CONFIG_LIVEUPDATE=y"
>>>>>
>>>>> # ./luo_multi_session
>>>>> 1..0 # SKIP Failed to open /dev/liveupdate. Is the luo module loaded?
>>>>>
>>>>> # ls /dev/liveupdate
>>>>> ls: cannot access '/dev/liveupdate': No such file or directory
>>>>>
>>>>> # grep "LIVEUPDATE" -inrHI /boot/config-`uname -r`
>>>>> /boot/config-next-20251107-luo+:349:CONFIG_LIVEUPDATE=y
>>>>> /boot/config-next-20251107-luo+:11985:CONFIG_LIVEUPDATE_TEST=y
>>>>>
>>>>> I made tests on FC42. But /dev/liveupdate is missing.
>>>> You need to add liveupdate=1 to your kernel cmdline to enable LUO and
>>>> get /dev/liveupdate.
>>> +1, kernel parameters require: kho=1 liveupdate=1
>>>
>>>> Pasha, your LUO series doesn't add the liveupdate parameter to
>>>> kernel-parameters.txt. I think it should be done in the next version to
>>>> this parameter is discoverable.
>>> Yeah, that is missing, I will update that in a standalone patch, or in
>>> a next version.
>>>
>>> Thanks,
>>> Pasha
>> --
>> Best Regards,
>> Yanjun.Zhu