x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 109 insertions, 0 deletions

diff --git a/Documentation/dev-tools/kunit/index.rst b/Documentation/dev-tools/kunit/index.rst
new file mode 100644
index 000000000..b3593ae29
--- /dev/null
+++ b/Documentation/dev-tools/kunit/index.rst
@@ -0,0 +1,109 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+KUnit - Linux Kernel Unit Testing
+=================================
+
+.. toctree::
+	:maxdepth: 2
+	:caption: Contents:
+
+	start
+	architecture
+	run_wrapper
+	run_manual
+	usage
+	api/index
+	style
+	faq
+	running_tips
+
+This section details the kernel unit testing framework.
+
+Introduction
+============
+
+KUnit (Kernel unit testing framework) provides a common framework for
+unit tests within the Linux kernel. Using KUnit, you can define groups
+of test cases called test suites. The tests either run on kernel boot
+if built-in, or load as a module. KUnit automatically flags and reports
+failed test cases in the kernel log. The test results appear in
+:doc:`KTAP (Kernel - Test Anything Protocol) format</dev-tools/ktap>`.
+It is inspired by JUnit, Python’s unittest.mock, and GoogleTest/GoogleMock
+(C++ unit testing framework).
+
+KUnit tests are part of the kernel, written in the C (programming)
+language, and test parts of the Kernel implementation (example: a C
+language function). Excluding build time, from invocation to
+completion, KUnit can run around 100 tests in less than 10 seconds.
+KUnit can test any kernel component, for example: file system, system
+calls, memory management, device drivers and so on.
+
+KUnit follows the white-box testing approach. The test has access to
+internal system functionality. KUnit runs in kernel space and is not
+restricted to things exposed to user-space.
+
+In addition, KUnit has kunit_tool, a script (``tools/testing/kunit/kunit.py``)
+that configures the Linux kernel, runs KUnit tests under QEMU or UML
+(:doc:`User Mode Linux </virt/uml/user_mode_linux_howto_v2>`),
+parses the test results and
+displays them in a user friendly manner.
+
+Features
+--------
+
+- Provides a framework for writing unit tests.
+- Runs tests on any kernel architecture.
+- Runs a test in milliseconds.
+
+Prerequisites
+-------------
+
+- Any Linux kernel compatible hardware.
+- For Kernel under test, Linux kernel version 5.5 or greater.
+
+Unit Testing
+============
+
+A unit test tests a single unit of code in isolation. A unit test is the finest
+granularity of testing and allows all possible code paths to be tested in the
+code under test. This is possible if the code under test is small and does not
+have any external dependencies outside of the test's control like hardware.
+
+
+Write Unit Tests
+----------------
+
+To write good unit tests, there is a simple but powerful pattern:
+Arrange-Act-Assert. This is a great way to structure test cases and
+defines an order of operations.
+
+- Arrange inputs and targets: At the start of the test, arrange the data
+  that allows a function to work. Example: initialize a statement or
+  object.
+- Act on the target behavior: Call your function/code under test.
+- Assert expected outcome: Verify that the result (or resulting state) is as
+  expected.
+
+Unit Testing Advantages
+-----------------------
+
+- Increases testing speed and development in the long run.
+- Detects bugs at initial stage and therefore decreases bug fix cost
+  compared to acceptance testing.
+- Improves code quality.
+- Encourages writing testable code.
+
+Read also :ref:`kinds-of-tests`.
+
+How do I use it?
+================
+
+You can find a step-by-step guide to writing and running KUnit tests in
+Documentation/dev-tools/kunit/start.rst
+
+Alternatively, feel free to look through the rest of the KUnit documentation,
+or to experiment with tools/testing/kunit/kunit.py and the example test under
+lib/kunit/kunit-example-test.c
+
+Happy testing!