Re: [PATCH] selftests: livepatch: unset sub_make_done in case top level Makefile be overwritten

[Zelin Deng <zelin.deng@linux.alibaba.com>]

在 2026/7/1 23:19, Thomas Weißschuh 写道:

> On Wed, Jul 01, 2026 at 05:14:24PM +0200, Petr Mladek wrote:
>> On Tue 2026-06-30 18:12:46, Thomas Weißschuh wrote:
>>> Hi Zelin,
>>>
>>> On Tue, Jun 30, 2026 at 04:32:16PM +0200, Petr Mladek wrote:
>>>> Added some people involved in "filechk_makefile" feature into Cc.
>>>>
>>>> For the new people, see the whole thread at
>>>> https://lore.kernel.org/all/20260525083721.27857-1-zelin.deng@linux.alibaba.com/
>>> Thanks for the report and forwarding it.
>>>
>>>> On Sun 2026-06-21 22:36:24, Zelin Deng wrote:
>>>>> 在 2026/6/19 22:42, Miroslav Benes 写道:
>>>>>> On Mon, 25 May 2026, Zelin Deng wrote:
>>>>> Here're how I reproduce the issue:
>>>>>
>>>>> 1. pull linux-next, reset to HEAD, for example
>>>>> 3ce97bd3c4f18608335e709c24d6a40e7036cab8 (tag next-20260619)
>>>>>
>>>>> 2. at linux-next tree: make all -j$(nproc) && make modules_install
>>>>> headers_install -j$(nproc) && make install && reboot
>>>>>
>>>>> 3. at linux-next tree: make kselftest-all
>>>>>
>>>>> 4. top level Makefile in linux-next has been overwritten by
>>>>>
>>>>>      export KBUILD_OUTPUT = .
>>>>>      export KBUILD_EXTMOD = /home/shiyu.dzl/linux-next
>>>>>      export KBUILD_EXTMOD_OUTPUT = /home/shiyu.dzl/linux-next
>>>>>      include /home/shiyu.dzl/linux-next/Makefile
>>>>>
>>>>> it is a stub generated by filechk_makefile.
>>>> It seems that "filechk_makefile" has reached mainline in v7.1-rc1,
>>>> see the commit c9bb03ac2c66bc5aa81b ("kbuild: reduce output spam when
>>>> building out of tree").
>>>>
>>>> The commit message says:
>>>>
>>>> <paste>
>>>>      The Makefile is now created even if the build is aborted due to an
>>>>      unclean working tree. That should not make a difference in practice.
>>>>   </paste>
>>>>
>>>> It seems that is actually makes a difference in the livepatch selftest
>>>> case.
>>>>
>>>> Sigh, the Makefile rules are a maze to me. It is possible that
>>>> we do something wrong in
>>>> tools/testing/selftests/livepatch/test_modules/Makefile. Namely
>>>> with:
>>>>
>>>> ifneq ("$(wildcard $(KDIR))", "")
>>>> 	$(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
>>>> endif
>>>>
>>>> But I see "$(MAKE) -C ..." called in many other makefiles.
>>>>
>>>> Best Regards,
>>>> Petr
>>>>
>>>>> I'm not quite sure that it could be related to my toolchain (like make
>>>>> version ?), I briefed analysis the root cause on my environment (KDIR
>>>>> '/lib/modules/7.1.0-next-20260619/build' which actually a symbol link to my
>>>>> kernel source -> '/home/shiyu.dzl/linux-next'):
>>>>>
>>>>>    1. sub_make_done leaks via environment. The top-level Makefile sets export
>>>>> sub_make_done := 1 after its first-pass initialization.
>>>>>    Because it is exported, every child make process inherits it.
>>>>>    2. livepatch test_modules re-invokes the top-level Makefile. The call
>>>>> chain is: top-level Makefile → kselftest-% pattern rule →
>>>>>    tools/testing/selftests/ → livepatch test_modules/Makefile → $(MAKE) -C
>>>>> $(KDIR) modules KBUILD_EXTMOD=..., which re-enters the top-level Makefile to
>>>>>    build an external module.
>>>>>    3. The inherited sub_make_done=1 skips critical initialization. The
>>>>> top-level Makefile's first-pass block (ifneq ($(sub_make_done),1)) is
>>>>>    skipped entirely. This block is responsible for correctly parsing
>>>>> command-line variables and setting up KBUILD_EXTMOD-related paths.
>>>>>    4. Path mismatch triggers false out-of-tree detection. With the
>>>>> initialization skipped, srcroot and CURDIR end up with mismatched values
>>>>> (e.g.,
>>>>>    absolute vs. relative). The comparison (ifeq ($(srcroot),$(CURDIR)))
>>>>> fails, so building_out_of_srctree is incorrectly set to 1.
>>>>>    5. outputmakefile overwrites the source tree's Makefile. Because
>>>>> building_out_of_srctree is set, the filechk_makefile rule fires and replaces
>>>>> the
>>>>>    real top-level Makefile with a generated stub containing KBUILD_OUTPUT,
>>>>> KBUILD_EXTMOD, and an include directive.
>>>>>
>>>>>    Why make -C tools/testing/selftests/ all is unaffected: it enters the
>>>>> selftests directory directly without ever executing the top-level Makefile
>>>>>    first, so sub_make_done is never exported into the environment. When
>>>>> livepatch test_modules later invokes $(MAKE) -C $(KDIR), the top-level
>>>>> Makefile
>>>>>    runs its full initialization normally.
>>> Can you try this:
>>>
>>> diff --git a/Makefile b/Makefile
>>> index b9c5792c79e0..f717a4dc96d6 100644
>>> --- a/Makefile
>>> +++ b/Makefile
>>> @@ -1591,10 +1591,10 @@ tools/%: FORCE
>>>   
>>>   PHONY += kselftest
>>>   kselftest: headers
>>> -	$(Q)$(MAKE) -C $(srctree)/tools/testing/selftests run_tests
>>> +	$(Q)unset sub_make_done; $(MAKE) -C $(srctree)/tools/testing/selftests run_tests
>>>   
>>>   kselftest-%: headers FORCE
>>> -	$(Q)$(MAKE) -C $(srctree)/tools/testing/selftests $*
>>> +	$(Q)unset sub_make_done; $(MAKE) -C $(srctree)/tools/testing/selftests $*
>>>   
>>>   PHONY += kselftest-merge
>>>   kselftest-merge:
>> Heh, this is exactly the same change which Zelin Deng proposed as
>> well, see
>> https://lore.kernel.org/all/20260525083721.27857-1-zelin.deng@linux.alibaba.com/
> The difference is that my proposal is in the toplevel Makefile while
> Zelin's is in the selftest one. The toplevel one should fix all selftests at
> the same time.
Thank you Petr. Yeah, Thomas's proposal is in top-level Makefile - if 
any other selftest also re-invokes the top-level Makefile with 
KBUILD_EXTMOD, it'd be covered too.
>
>>> The same is done for cmd_install.
>> I guess that this is related to the commit 14ccc638b02f9ec ("kbuild:
>> cancel sub_make_done for the install target to fix DKMS"). Which
>> is related to the commit bcf637f54f6d2515d ("kbuild: parse C= and M=
>> before changing the working directory").
>>
>> Honestly, it all looks like a wild magic to me. I would need much
>> better understanding of the Makefile maze to get on top of it.
> I was not able to reproduce the issue yet. My proposal is just a guess.
> We'll need feedback from Zelin.

I had verify your proposal, it worked well - liveupatch kmod was built 
successfully and top-level Makefile wasn't overwritten any more.

Petr thank you for your Ack, I think Thomas's proposal is better than 
mine, we don't have to do the quirk everytime when new selftest kmod is 
added.

Thomas, so do I have to send a updated patch or you will do it by youself?

>
>> But it seems that it is a reasonable fix after all. It solves the
>> original problem. It does not break my workflow. So, I tend to add:
>>
>> Acked-by: Petr Mladek <pmladek@suse.com>
>
> Thomas