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/drivers/tc/tc-driver.c b/drivers/tc/tc-driver.c
new file mode 100644
index 000000000..2f6d14759
--- /dev/null
+++ b/drivers/tc/tc-driver.c
@@ -0,0 +1,109 @@
+/*
+ *	TURBOchannel driver services.
+ *
+ *	Copyright (c) 2005  James Simmons
+ *	Copyright (c) 2006  Maciej W. Rozycki
+ *
+ *	Loosely based on drivers/dio/dio-driver.c and
+ *	drivers/pci/pci-driver.c.
+ *
+ *	This file is subject to the terms and conditions of the GNU
+ *	General Public License.  See the file "COPYING" in the main
+ *	directory of this archive for more details.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/tc.h>
+
+/**
+ * tc_register_driver - register a new TC driver
+ * @drv: the driver structure to register
+ *
+ * Adds the driver structure to the list of registered drivers
+ * Returns a negative value on error, otherwise 0.
+ * If no error occurred, the driver remains registered even if
+ * no device was claimed during registration.
+ */
+int tc_register_driver(struct tc_driver *tdrv)
+{
+	return driver_register(&tdrv->driver);
+}
+EXPORT_SYMBOL(tc_register_driver);
+
+/**
+ * tc_unregister_driver - unregister a TC driver
+ * @drv: the driver structure to unregister
+ *
+ * Deletes the driver structure from the list of registered TC drivers,
+ * gives it a chance to clean up by calling its remove() function for
+ * each device it was responsible for, and marks those devices as
+ * driverless.
+ */
+void tc_unregister_driver(struct tc_driver *tdrv)
+{
+	driver_unregister(&tdrv->driver);
+}
+EXPORT_SYMBOL(tc_unregister_driver);
+
+/**
+ * tc_match_device - tell if a TC device structure has a matching
+ *                   TC device ID structure
+ * @tdrv: the TC driver to earch for matching TC device ID strings
+ * @tdev: the TC device structure to match against
+ *
+ * Used by a driver to check whether a TC device present in the
+ * system is in its list of supported devices.  Returns the matching
+ * tc_device_id structure or %NULL if there is no match.
+ */
+static const struct tc_device_id *tc_match_device(const struct tc_driver *tdrv,
+						  struct tc_dev *tdev)
+{
+	const struct tc_device_id *id = tdrv->id_table;
+
+	if (id) {
+		while (id->name[0] || id->vendor[0]) {
+			if (strcmp(tdev->name, id->name) == 0 &&
+			    strcmp(tdev->vendor, id->vendor) == 0)
+				return id;
+			id++;
+		}
+	}
+	return NULL;
+}
+
+/**
+ * tc_bus_match - Tell if a device structure has a matching
+ *                TC device ID structure
+ * @dev: the device structure to match against
+ * @drv: the device driver to search for matching TC device ID strings
+ *
+ * Used by a driver to check whether a TC device present in the
+ * system is in its list of supported devices.  Returns 1 if there
+ * is a match or 0 otherwise.
+ */
+static int tc_bus_match(struct device *dev, const struct device_driver *drv)
+{
+	struct tc_dev *tdev = to_tc_dev(dev);
+	const struct tc_driver *tdrv = to_tc_driver(drv);
+	const struct tc_device_id *id;
+
+	id = tc_match_device(tdrv, tdev);
+	if (id)
+		return 1;
+
+	return 0;
+}
+
+const struct bus_type tc_bus_type = {
+	.name	= "tc",
+	.match	= tc_bus_match,
+};
+EXPORT_SYMBOL(tc_bus_type);
+
+static int __init tc_driver_init(void)
+{
+	return bus_register(&tc_bus_type);
+}
+
+postcore_initcall(tc_driver_init);