[PATCH v2 1/2] selftests: run tests on nommu architecture
Lorenzo Stoakes (ARM)
ljs at kernel.org
Tue Aug 25 06:36:22 PDT 2026
On Tue, Aug 25, 2026 at 10:59:44AM +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 build stage, add -DCONFIG_NOMMU to CFLAGS when NOMMU=1 variable
> added to the build/make argument.
> - 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.
> - kselftest_harness.h: skip the tests if the file is include when
> executing on NOMMU platform, as there is no fork(2) syscall.
> - replace "cd -" use as it is not available a shell supported on nommu
> (e.g., busybox hush), use cd "$OLDDIR" instead.
> - 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=mm/nommu
> $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=mm/nommu
> $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p \
> -c mm/nommu
>
> Cc: Shuah Khan <shuah at kernel.org>
> Cc: Jonathan Corbet <corbet at lwn.net>
> Cc: Kees Cook <kees at kernel.org>
> Cc: Andy Lutomirski <luto at amacapital.net>
> Cc: Will Drewry <wad at chromium.org>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Brendan Jackman <brendan.jackman at linux.dev>
> Cc: Hangbin Liu <liuhangbin at gmail.com>
> Cc: "Ricardo B. Marliere" <rbm at suse.com>
> Cc: linux-kselftest at vger.kernel.org
> Cc: linux-um at lists.infradead.org
> Cc: linux-mm at kvack.org
> Cc: linux-doc at vger.kernel.org
> Closes: https://sashiko.dev/#/patchset/20260813063401.1786548-1-thehajime%40gmail.com
> Signed-off-by: Hajime Tazaki <thehajime at gmail.com>
Doesn't seem too crazy, but some nitty comments below.
>
> --
>
> rfc => v2
> - reformat ktap header, reported by Sashiko review
>
> 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 | 9 +++++++--
> tools/testing/selftests/kselftest_harness.h | 4 ++++
> tools/testing/selftests/lib.mk | 8 ++++++++
> 4 files changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/dev-tools/kselftest.rst b/Documentation/dev-tools/kselftest.rst
> index 64c0ec7428a2..a65f3ebc5906 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=mm/nommu # <= build-only
> + $ make ARCH=um NOMMU=1 O=build kselftest-install TARGETS=mm/nommu
> + $ NOMMU=1 ./build/kselftest/kselftest_install/run_kselftest.sh -p -c mm/nommu
> +
> Contributing new tests
> ======================
>
> diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
> index 311811dc55a0..7287d8290b6c 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
> @@ -130,6 +134,7 @@ run_one()
> return $KSFT_FAIL
> fi
> fi
> + OLDDIR=$(pwd)
> cd `dirname $TEST` > /dev/null
> (((( tap_timeout "$cmd" 2>&1; echo $? >&3) |
> tap_prefix >&4) 3>&1) |
> @@ -147,7 +152,7 @@ run_one()
> *)
> ktap_test_fail "$TEST_HDR_MSG # exit=$rc";;
> esac
> - cd - >/dev/null
> + cd "$OLDDIR" >/dev/null
Hmm, why are you changing this bit?
> fi
>
> return $rc
> diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
> index 261e4df94d9d..0d05946a5e7a 100644
> --- a/tools/testing/selftests/kselftest_harness.h
> +++ b/tools/testing/selftests/kselftest_harness.h
> @@ -1274,6 +1274,10 @@ static int test_harness_run(int argc, char **argv)
> unsigned int count = 0;
> unsigned int pass_count = 0;
>
> +#ifdef CONFIG_NOMMU
Let's not prefix with CONFIG_ :) I think this is pretty confusing vs. the kernel
CONFIG_xxx flags, esp. as this obviously inverts CONFIG_MMU.
maybe just 'NOMMU'?
> + ksft_print_header();
> + ksft_exit_skip("kselftest harness requires fork(2), unavailable on NOMMU\n");
> +#endif /* CONFIG_NOMMU */
> ret = test_harness_argv_check(argc, argv);
> if (ret != KSFT_PASS)
> return ret;
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index f02cc8a2e4ae..fdb895967768 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -97,6 +97,14 @@ TEST_GEN_PROGS := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_PROGS))
> TEST_GEN_PROGS_EXTENDED := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_PROGS_EXTENDED))
> TEST_GEN_FILES := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_FILES))
>
> +# detect if users request NOMMU build or not
> +# User can set NOMMU to 1 to build/test for NOMMU platforms
> +NOMMU ?= 0
> +ifeq ($(NOMMU),1)
> +CFLAGS += -DCONFIG_NOMMU
> +export NOMMU
> +endif
> +
I wonder if this could be put into testing/selftests/nommu/something.mk? Though
I guess would have to be included for all builds to account for nommu trying to
build any kind of tests.
> all: $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES) \
> $(if $(TEST_GEN_MODS_DIR),gen_mods_dir)
>
> --
> 2.43.0
>
--
Cheers, Lorenzo
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