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

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/[email protected]/

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:
> > > 
> > > > After I did: make kselftest-all in top level of kernel source tree, top
> > > > level Makefile was overwritten by auto generated contents by
> > > > filechk_makefile:
> > > > [root@emr: /home/shiyu.dzl/linux-next]$ cat Makefile
> > > > 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
> > > > 
> > > > Top-level Makefile export sub_make_done=1, leaks into unrelated re-invocations
> > > > of the top-level Makefile when recursive descent through selftests -
> > > > building test_module of livepatch. That causes KBUILD_EXTMOD setup to be
> > > > skipped, which leads to a relative/absolute path mismatch in srcroot vs
> > > > CURDIR, falsely setting building_out_of_srctree, and ultimately overwriting
> > > > the source tree's Makefile with a generated stub.
> > > > 
> > > > Clear sub_make_done before re-invoking the kernel Makefile.
> > > > 
> > > > Fixes: c4bbe83d27c2 ("livepatch: Move tests from lib/livepatch to selftests/livepatch")
> > > > Signed-off-by: Zelin Deng <[email protected]>
> > > Adding Marcos and KLP ML.
> > > 
> > > I cannot reproduce and I do not understand it much from the changelog (I
> > > am by far not a Kbuild expert). Could you share the exact steps to
> > > reproduce please? If I just run 'make kselftest-all' in the top level, it
> > > passes and livepatch test_modules are not even touched.
> > > 
> > > Miroslav
> > 
> > Thank you for replying.
> > 
> > Per my understanding, to build livepatch test_modules KDIR must be either
> > set explicitly when doing 'make kselftest-all
> > KDIR=<path-to-kernel-build-dir>' or have the kernel devel package installed.
> > Otherwise the compilation could be skipped. (see
> > tools/testing/selftests/livepatch/test_modules/Makefile)
> > 
> > KDIR ?= /lib/modules/$(shell uname -r)/build
> > 
> > ...
> > 
> > # Ensure that KDIR exists, otherwise skip the compilation
> > modules:
> > ifneq ("$(wildcard $(KDIR))", "")
> >     $(Q)$(MAKE) -C $(KDIR) modules KBUILD_EXTMOD=$(TESTMODS_DIR)
> > endif
> > 
> > ...
> > 
> > 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:

The same is done for cmd_install.


Thomas