lkdtm: basic description

Author: pvts-mat

kselftests/lkdtm/README.rst

@@ -0,0 +1,162 @@
+About
+=====
+
+LKDTM (Linux Kernel Dump Test Module) is used for crashing the kernel on
+demand and checking whether the kernel handled this properly.
+
+Related files
+=============
+
+``Documentation/fault-injection/provoke-crashes.rst``
+-----------------------------------------------------
+
+Describes the ``lkdtm`` module allowing for provoked kernel crashes.
+
+The collection's test names correspond to the ``cpoint_type`` ("crash
+point type") values mentioned in that document.
+
+``tools/testing/selftests/lkdtm/tests.txt``
+-------------------------------------------
+
+List of the actual tests contained in the collection, with some
+meta-data attached. The mapping:
+
+::
+
+   #PANIC
+   BUG kernel BUG at
+   WARNING WARNING:
+   WARNING_MESSAGE message trigger
+   EXCEPTION
+   #LOOP Hangs the system
+   #EXHAUST_STACK Corrupts memory on failure
+   #CORRUPT_STACK Crashes entire system on success
+   #CORRUPT_STACK_STRONG Crashes entire system on success
+   …
+
+->
+
+::
+
+   lkdtm:PANIC.sh
+   lkdtm:BUG.sh
+   lkdtm:WARNING.sh
+   lkdtm:WARNING_MESSAGE.sh
+   lkdtm:EXCEPTION.sh
+   lkdtm:LOOP.sh
+   lkdtm:EXHAUST_STACK.sh
+   lkdtm:CORRUPT_STACK.sh
+   lkdtm:CORRUPT_STACK_STRONG.sh
+   …
+
+#. The lines starting with ``#`` aren't really comments, in a sense that
+   whatever follows the ``#`` isn't ignored - it does in fact specify a
+   test, but it will be reported as skipped when executed. The
+   "dangerous" tests are commented out by default.
+
+#. When a line contains multiple words only the first one is used as the
+   test's name.
+
+   ::
+
+      BUDDY_INIT_ON_ALLOC Memory appears initialized
+
+   ->
+
+   ::
+
+      lkdtm:BUDDY_INIT_ON_ALLOC.sh
+
+   The rest is used as a short *note* about what is to be expected from
+   this test, displayed upon the test execution. It's also what's being
+   searched for in dmesg after provoking the failure, as a test's
+   success criterion.
+
+``tools/testing/selftests/lkdtm/run.sh``
+----------------------------------------
+
+The template for each test in the collection. Although the test names
+like ``lkdtm:WARNING_MESSAGE.sh`` suggest there is a shell script for
+each of them there is in fact only one - the ``run.sh`` - which is
+copied multiple times inside the ``tools/testing/selftests/lkdtm/``
+directory with different names corresponding to different test names
+when the ``lkdtm`` collection is build. Each script then, when run,
+introspects its own name to know which test it should conduct and then
+just writes the test's name into the
+``/sys/kernel/debug/provoke-crash/DIRECT``, like
+
+.. code:: shell
+
+   echo ‹test› > /sys/kernel/debug/provoke-crash/DIRECT
+
+After that the newly shown dmesg lines are searched for the test's note,
+or for "call trace:" if it doesn't have any. If the text was found the
+test reports success, otherwise failure.
+
+For example, the ``lkdtm:WARNING_MESSAGE.sh`` test is realized by
+``tools/testing/selftests/lkdtm/WARNING_MESSAGE.sh``, copied from
+``tools/testing/selftests/lkdtm/run.sh``, which writes
+
+.. code:: shell
+
+   echo WARNING_MESSAGE > /sys/kernel/debug/provoke-crash/DIRECT
+
+Then the dmesg is searched for "message trigger", as that is the
+``WARNING_MESSAGE``'s note defined in the
+`tools/testing/selftests/lkdtm/tests.txt`_
+
+``tools/testing/selftests/lkdtm/stack-entropy.sh``
+--------------------------------------------------
+
+Corresponds to the ``lkdtm:stack-entropy.sh`` test, the only one not
+realized by the ``run.sh`` script.
+
+Requirements and applicability
+==============================
+
+The ``lkdtm`` collection is not available in pre-``9.2`` versions. The
+tests don't have any compilation requirements, but to run them the
+``lkdtm`` module has to be available in the tested kernel, provided by
+the ``CONFIG_LKDTM`` option, which is disabled in all default
+configurations of LTS versions ``9.2``, ``9.4`` (other not checked)
+
+.. code:: shell
+
+   grep CONFIG_LKDTM kernel-src-tree-{ciqlts9_2,ciqlts9_4}/configs/kernel*.config
+
+::
+
+   kernel-src-tree-ciqlts9_2/configs/kernel-aarch64-64k-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-aarch64-64k-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-aarch64-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-aarch64-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-ppc64le-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-ppc64le-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-s390x-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-s390x-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-s390x-zfcpdump-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-x86_64-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_2/configs/kernel-x86_64-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-64k-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-64k-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-rt-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-aarch64-rt-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-ppc64le-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-ppc64le-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-s390x-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-s390x-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-s390x-zfcpdump-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-x86_64-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-x86_64-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-x86_64-rt-debug-rhel.config:# CONFIG_LKDTM is not set
+   kernel-src-tree-ciqlts9_4/configs/kernel-x86_64-rt-rhel.config:# CONFIG_LKDTM is not set
+
+This does not mean that these tests don't apply to Rocky Linux in
+general (disabling ``CONFIG_LKDTM`` does not eliminate potentially
+malfunctioning code branches, only the way to expose them), but it
+certainly doesn't make sense to run them on the default builds.
+
+Note that for full functionality also other options may need to be
+enabled - see the ``tools/testing/selftests/lkdtm/config`` file.