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

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

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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.

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

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