Re: [PATCH v3 2/3] selftests: run tests on nommu architecture

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Sat, Sep 26, 2026 at 10:08:18AM +0900, Hajime Tazaki wrote:
> Architectures lacks MMU doesn't support fork(2) syscall and only
> vfork(2) is available with limitations.  Thus, we cannot run kselftest
> on nommu architecture as is.
>
> This commit addresses this issue with the following changes:
>
> - on test run stage, avoid calling timeout command when NOMMU=1 variable
>   added to environmental variable, since timeout command uses fork
>   syscall which nommu platform doesn't support.
> - describe the difference of nommu tests in the document.
>
> So command line to build/execute tests for nommu should be like below:
>
>  $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu
>  $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
>  $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p \
>    -c nommu
>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Kees Cook <kees@kernel.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Will Drewry <wad@chromium.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Brendan Jackman <brendan.jackman@linux.dev>
> Cc: Hangbin Liu <liuhangbin@gmail.com>
> Cc: "Ricardo B. Marliere" <rbm@suse.com>
> Cc: linux-kselftest@vger.kernel.org
> Cc: linux-um@lists.infradead.org
> Cc: linux-mm@kvack.org
> Cc: linux-doc@vger.kernel.org
> Closes: https://sashiko.dev/#/patchset/20260813063401.1786548-1-thehajime%40gmail.com
> Signed-off-by: Hajime Tazaki <thehajime@gmail.com>

LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

>
> --
>
> v2 => v3
> - remove unnecessary modification
> - new target is moved from TARGETS=mm/nommu to TARGETS=nommu
> - rename CONFIG_NOMMU to NOMMU to avoid confusion to kernel config
>
> rfc => v2
> - reformat ktap header, reported by Sashiko review
> - https://lore.kernel.org/linux-mm/20260825015945.141739-2-thehajime@gmail.com/
>
> rfc: https://lore.kernel.org/linux-mm/20260813063401.1786548-1-thehajime@gmail.com/
> ---
>  Documentation/dev-tools/kselftest.rst       | 14 ++++++++++++++
>  tools/testing/selftests/kselftest/runner.sh |  6 +++++-
>  2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst
> index 64c0ec7428a2..c35b819947b7 100644
> --- a/Documentation/dev-tools/kselftest.rst
> +++ b/Documentation/dev-tools/kselftest.rst
> @@ -230,6 +230,20 @@ section::
>
>  .. _tar's auto-compress: https://www.gnu.org/software/tar/manual/html_node/gzip.html#auto_002dcompress
>
> +Build and test on nommu target
> +==============================
> +
> +If you (cross-)build kselftests for nommu targets, or run tests on nommu targets, use
> +``NOMMU=1`` as a make variable/environment setting to tell build system to do the additional
> +checks.  These nommu targets may differ in several ways, such as not supporting fork(2) or
> +using musl or another libc.  Set this variable to apply the necessary build and test adjustments.
> +
> +::
> +
> +  $ make ARCH=um NOMMU=1 O=build kselftest-all TARGETS=nommu  # <= build-only
> +  $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=nommu
> +  $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p -c nommu
> +
>  Contributing new tests
>  ======================
>
> diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
> index 8fc1018d6fec..95b5ebb8bbb9 100644
> --- a/tools/testing/selftests/kselftest/runner.sh
> +++ b/tools/testing/selftests/kselftest/runner.sh
> @@ -38,8 +38,12 @@ tap_prefix()
>
>  tap_timeout()
>  {
> +	# nommu doesn't support timeout command (missing fork(2))
> +	if [ "$NOMMU" = "1" ] ; then
> +		echo "timeout isn't supported for NOMMU"
> +		$1
>  	# Make sure tests will time out if utility is available.
> -	if [ -x /usr/bin/timeout ] ; then
> +	elif [ -x /usr/bin/timeout ] ; then
>  		/usr/bin/timeout --foreground "$kselftest_timeout" \
>  			/usr/bin/timeout "$kselftest_timeout" $1
>  	else
> --
> 2.43.0
>

--
Cheers, Lorenzo