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, 81 insertions, 0 deletions

diff --git a/drivers/of/module.c b/drivers/of/module.c
new file mode 100644
index 000000000..1e735fc13
--- /dev/null
+++ b/drivers/of/module.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Linux kernel module helpers.
+ */
+
+#include <linux/of.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
+{
+	const char *compat;
+	char *c;
+	struct property *p;
+	ssize_t csize;
+	ssize_t tsize;
+
+	/*
+	 * Prevent a kernel oops in vsnprintf() -- it only allows passing a
+	 * NULL ptr when the length is also 0. Also filter out the negative
+	 * lengths...
+	 */
+	if ((len > 0 && !str) || len < 0)
+		return -EINVAL;
+
+	/* Name & Type */
+	/* %p eats all alphanum characters, so %c must be used here */
+	csize = snprintf(str, len, "of:N%pOFn%c%s", np, 'T',
+			 of_node_get_device_type(np));
+	tsize = csize;
+	if (csize >= len)
+		csize = len > 0 ? len - 1 : 0;
+	len -= csize;
+	str += csize;
+
+	of_property_for_each_string(np, "compatible", p, compat) {
+		csize = snprintf(str, len, "C%s", compat);
+		tsize += csize;
+		if (csize >= len)
+			continue;
+		for (c = str; c; ) {
+			c = strchr(c, ' ');
+			if (c)
+				*c++ = '_';
+		}
+		len -= csize;
+		str += csize;
+	}
+
+	return tsize;
+}
+
+int of_request_module(const struct device_node *np)
+{
+	char *str;
+	ssize_t size;
+	int ret;
+
+	if (!np)
+		return -ENODEV;
+
+	size = of_modalias(np, NULL, 0);
+	if (size < 0)
+		return size;
+
+	/* Reserve an additional byte for the trailing '\0' */
+	size++;
+
+	str = kmalloc(size, GFP_KERNEL);
+	if (!str)
+		return -ENOMEM;
+
+	of_modalias(np, str, size);
+	str[size - 1] = '\0';
+	ret = request_module(str);
+	kfree(str);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(of_request_module);