The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh'
depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs
while checking reservations asynchronously in the background.

When this binary is missing (e.g., excluded from the build), these tests hang
for up to 180 seconds. During this time, run_vmtests.sh is eventually killed
due to timeout, aborting all subsequent tests.

This patch skips these tests if the binary is not found, preventing delays
and ensuring that the test suite runs to completion.

Signed-off-by: Khaled Elnaggar <khaledelnaggarlinux@gmail.com>
---
 tools/testing/selftests/mm/run_vmtests.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index dddd1dd8af14..0b55395ee2cb 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -375,8 +375,13 @@ CATEGORY="process_mrelease" run_test ./mrelease_test
 CATEGORY="mremap" run_test ./mremap_test

 CATEGORY="hugetlb" run_test ./thuge-gen
+
+# the following tests depend on write_to_hugetlbfs binary
+if [ -x ./write_to_hugetlbfs ]; then
 CATEGORY="hugetlb" run_test ./charge_reserved_hugetlb.sh -cgroup-v2
 CATEGORY="hugetlb" run_test ./hugetlb_reparenting_test.sh -cgroup-v2
+fi
+
 if $RUN_DESTRUCTIVE; then
 nr_hugepages_tmp=$(cat /proc/sys/vm/nr_hugepages)
 enable_soft_offline=$(cat /proc/sys/vm/enable_soft_offline)
--
2.47.2

On Tue,  3 Jun 2025 02:22:32 +0300 Khaled Elnaggar <khaledelnaggarlinux@gmail.com> wrote:

> The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh'
> depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs
> while checking reservations asynchronously in the background.
> 
> When this binary is missing (e.g., excluded from the build), these tests hang
> for up to 180 seconds. During this time, run_vmtests.sh is eventually killed
> due to timeout, aborting all subsequent tests.
> 
> This patch skips these tests if the binary is not found, preventing delays
> and ensuring that the test suite runs to completion.

OK, but why is write_to_hugetlbfs missing?  If we're in a situation
where we _could_ run it then we _should_ run it!  The user wants to
test stuff so we should test as much as we can.

So I'm thinking that it would be preferable to make sure the dang thing
is there?

On 03/06/2025 5:12 am, Andrew Morton wrote:
> On Tue,  3 Jun 2025 02:22:32 +0300 Khaled Elnaggar <khaledelnaggarlinux@gmail.com> wrote:
> 
>> The hugevm tests 'charge_reserved_hugetlb.sh' and 'hugetlb_reparenting_test.sh'
>> depend on the 'write_to_hugetlbfs' binary to simulate writes to hugetlbfs
>> while checking reservations asynchronously in the background.
>>
>> When this binary is missing (e.g., excluded from the build), these tests hang
>> for up to 180 seconds. During this time, run_vmtests.sh is eventually killed
>> due to timeout, aborting all subsequent tests.
>>
>> This patch skips these tests if the binary is not found, preventing delays
>> and ensuring that the test suite runs to completion.
> 
> OK, but why is write_to_hugetlbfs missing?  If we're in a situation
> where we _could_ run it then we _should_ run it!  The user wants to
> test stuff so we should test as much as we can.
> So I'm thinking that it would be preferable to make sure the dang thing
> is there?
> 

Totally agree, let me try to explain how I understand the issue.

The write_to_hugetlbfs binary is built from selftests/mm/Makefile,
lines 136–142. It is only compiled if ARCH matches one of the explicitly
listed 64-bit architectures:


```
   ifneq (,$(filter $(ARCH),arm64 mips64 parisc64 powerpc riscv64 s390x sparc64 x86_64 s390))
   TEST_GEN_FILES += va_high_addr_switch
   ifneq ($(ARCH),riscv64)
   TEST_GEN_FILES += virtual_address_range
   endif
   TEST_GEN_FILES += write_to_hugetlbfs
   endif
```

However, when the MM selftests are run from the kernel’s top-level Makefile,
(root directory for example:

  make defconfig
  sudo make kselftest TARGETS=mm


ARCH is resolved as x86, even on an x86_64 machine (Debian in my case),
ARCH=x86 is the reason why the binary gets excluded from the build system.

As far as I understand, the top-level Makefile normalizes both
i.86 and x86_64 to x86 for ARCH variable:

Makfile: lines: 383,403
        383:include $(srctree)/scripts/subarch.include
        403:ARCH                ?= $(SUBARCH)

scripts/subarch.include: line: 7
        7:SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \

This mapping probably makes sense for selecting the correct arch/ directory
(since we have arch/x86, not arch/x86_64) for top-level Makefile.

But the mm selftests Makefile expects ARCH to differentiate between x86 and x86_64
to decide whether to build certain binaries.
As a result, the 64-bit-only binaries like write_to_hugetlbfs are skipped
during build, yet still expected at runtime (by run_vmtests.sh).

That's why this whole issue of the missing executable does not happen when
ran from selftests/mm using something like:

  sudo make -C tools/testing/selftests/mm

Because then selftests/mm/Makefile arch detection rus as intended.

You're right — the proper fix is to improve how we propagate architecture
information from the top-level Makefile to selftests.
But since that's a larger change (and possibly beyond what I can safely
attempt at this point), this patch is just a targeted workaround to
avoid test stalls when the binary is missing.

I hope I haven't gone completely wrong with this analysis, happy to improve
or revise it further if needed.