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, 123 insertions, 0 deletions

diff --git a/lib/kunit/static_stub.c b/lib/kunit/static_stub.c
new file mode 100644
index 000000000..d9dd6377a
--- /dev/null
+++ b/lib/kunit/static_stub.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit function redirection (static stubbing) API.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: David Gow <davidgow@google.com>
+ */
+
+#include <kunit/test.h>
+#include <kunit/static_stub.h>
+#include "hooks-impl.h"
+
+
+/* Context for a static stub. This is stored in the resource data. */
+struct kunit_static_stub_ctx {
+	void *real_fn_addr;
+	void *replacement_addr;
+};
+
+static void __kunit_static_stub_resource_free(struct kunit_resource *res)
+{
+	kfree(res->data);
+}
+
+/* Matching function for kunit_find_resource(). match_data is real_fn_addr. */
+static bool __kunit_static_stub_resource_match(struct kunit *test,
+						struct kunit_resource *res,
+						void *match_real_fn_addr)
+{
+	/* This pointer is only valid if res is a static stub resource. */
+	struct kunit_static_stub_ctx *ctx = res->data;
+
+	/* Make sure the resource is a static stub resource. */
+	if (res->free != &__kunit_static_stub_resource_free)
+		return false;
+
+	return ctx->real_fn_addr == match_real_fn_addr;
+}
+
+/* Hook to return the address of the replacement function. */
+void *__kunit_get_static_stub_address_impl(struct kunit *test, void *real_fn_addr)
+{
+	struct kunit_resource *res;
+	struct kunit_static_stub_ctx *ctx;
+	void *replacement_addr;
+
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+
+	if (!res)
+		return NULL;
+
+	ctx = res->data;
+	replacement_addr = ctx->replacement_addr;
+	kunit_put_resource(res);
+	return replacement_addr;
+}
+
+void kunit_deactivate_static_stub(struct kunit *test, void *real_fn_addr)
+{
+	struct kunit_resource *res;
+
+	KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
+				"Tried to deactivate a NULL stub.");
+
+	/* Look up the existing stub for this function. */
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+
+	/* Error out if the stub doesn't exist. */
+	KUNIT_ASSERT_PTR_NE_MSG(test, res, NULL,
+				"Tried to deactivate a nonexistent stub.");
+
+	/* Free the stub. We 'put' twice, as we got a reference
+	 * from kunit_find_resource()
+	 */
+	kunit_remove_resource(test, res);
+	kunit_put_resource(res);
+}
+EXPORT_SYMBOL_GPL(kunit_deactivate_static_stub);
+
+/* Helper function for kunit_activate_static_stub(). The macro does
+ * typechecking, so use it instead.
+ */
+void __kunit_activate_static_stub(struct kunit *test,
+				  void *real_fn_addr,
+				  void *replacement_addr)
+{
+	struct kunit_static_stub_ctx *ctx;
+	struct kunit_resource *res;
+
+	KUNIT_ASSERT_PTR_NE_MSG(test, real_fn_addr, NULL,
+				"Tried to activate a stub for function NULL");
+
+	/* If the replacement address is NULL, deactivate the stub. */
+	if (!replacement_addr) {
+		kunit_deactivate_static_stub(test, real_fn_addr);
+		return;
+	}
+
+	/* Look up any existing stubs for this function, and replace them. */
+	res = kunit_find_resource(test,
+				  __kunit_static_stub_resource_match,
+				  real_fn_addr);
+	if (res) {
+		ctx = res->data;
+		ctx->replacement_addr = replacement_addr;
+
+		/* We got an extra reference from find_resource(), so put it. */
+		kunit_put_resource(res);
+	} else {
+		ctx = kmalloc_obj(*ctx);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
+		ctx->real_fn_addr = real_fn_addr;
+		ctx->replacement_addr = replacement_addr;
+		res = kunit_alloc_resource(test, NULL,
+				     &__kunit_static_stub_resource_free,
+				     GFP_KERNEL, ctx);
+	}
+}
+EXPORT_SYMBOL_GPL(__kunit_activate_static_stub);