[PATCH v2] Documentation: kunit: Add some troubleshooting tips to the FAQ

From: David Gow
Date: Tue Jun 02 2020 - 23:37:54 EST

Add an FAQ entry to the KUnit documentation with some tips for
troubleshooting KUnit and kunit_tool.

These suggestions largely came from an email thread:

Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Reviewed-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
Changes since v1[1]
- Added a section about running KUnit outside UML (based heavily on
Alan's suggestion in the thread).

[1]: https://lore.kernel.org/linux-kselftest/20200602054216.93122-1-davidgow@xxxxxxxxxx/

Documentation/dev-tools/kunit/faq.rst | 40 +++++++++++++++++++++++++++
1 file changed, 40 insertions(+)

diff --git a/Documentation/dev-tools/kunit/faq.rst b/Documentation/dev-tools/kunit/faq.rst
index ea55b2467653..1628862e7024 100644
--- a/Documentation/dev-tools/kunit/faq.rst
+++ b/Documentation/dev-tools/kunit/faq.rst
@@ -61,3 +61,43 @@ test, or an end-to-end test.
kernel by installing a production configuration of the kernel on production
hardware with a production userspace and then trying to exercise some behavior
that depends on interactions between the hardware, the kernel, and userspace.
+KUnit isn't working, what should I do?
+Unfortunately, there are a number of things which can break, but here are some
+things to try.
+1. Try running ``./tools/testing/kunit/kunit.py run`` with the ``--raw_output``
+ parameter. This might show details or error messages hidden by the kunit_tool
+ parser.
+2. Instead of running ``kunit.py run``, try running ``kunit.py config``,
+ ``kunit.py build``, and ``kunit.py exec`` independently. This can help track
+ down where an issue is occurring. (If you think the parser is at fault, you
+ can run it manually against stdin or a file with ``kunit.py parse``.)
+3. Running the UML kernel directly can often reveal issues or error messages
+ kunit_tool ignores. This should be as simple as running ``./vmlinux`` after
+ building the UML kernel (e.g., by using ``kunit.py build``). Note that UML
+ has some unusual requirements (such as the host having a tmpfs filesystem
+ mounted), and has had issues in the past when built statically and the host
+ has KASLR enabled. (On older host kernels, you may need to run ``setarch
+ `uname -m` -R ./vmlinux`` to disable KASLR.)
+4. Make sure the kernel .config has ``CONFIG_KUNIT=y`` and at least one test
+ (e.g. ``CONFIG_KUNIT_EXAMPLE_TEST=y``). kunit_tool will keep its .config
+ around, so you can see what config was used after running ``kunit.py run``.
+ It also preserves any config changes you might make, so you can
+ enable/disable things with ``make ARCH=um menuconfig`` or similar, and then
+ re-run kunit_tool.
+5. Try to run ``make ARCH=um defconfig`` before running ``kunit.py run``. This
+ may help clean up any residual config items which could be causing problems.
+6. Finally, try running KUnit outside UML. KUnit and KUnit tests can run be
+ built into any kernel, or can be built as a module and loaded at runtime.
+ Doing so should allow you to determine if UML is causing the issue you're
+ seeing. When tests are built-in, they will execute when the kernel boots, and
+ modules will automatically execute associated tests when loaded. Test results
+ can be collected from ``/sys/kernel/debug/kunit/<test suite>/results``, and
+ can be parsed with ``kunit.py parse``. For more details, see "KUnit on
+ non-UML architectures" in :doc:`usage`.
+If none of the above tricks help, you are always welcome to email any issues to