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, 95 insertions, 0 deletions

diff --git a/lib/argv_split.c b/lib/argv_split.c
new file mode 100644
index 000000000..e28db8e3b
--- /dev/null
+++ b/lib/argv_split.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Helper function for splitting a string into an argv-like array.
+ */
+
+#include <linux/kernel.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+
+static int count_argc(const char *str)
+{
+	int count = 0;
+	bool was_space;
+
+	for (was_space = true; *str; str++) {
+		if (isspace(*str)) {
+			was_space = true;
+		} else if (was_space) {
+			was_space = false;
+			count++;
+		}
+	}
+
+	return count;
+}
+
+/**
+ * argv_free - free an argv
+ * @argv: the argument vector to be freed
+ *
+ * Frees an argv and the strings it points to.
+ */
+void argv_free(char **argv)
+{
+	argv--;
+	kfree(argv[0]);
+	kfree(argv);
+}
+EXPORT_SYMBOL(argv_free);
+
+/**
+ * argv_split - split a string at whitespace, returning an argv
+ * @gfp: the GFP mask used to allocate memory
+ * @str: the string to be split
+ * @argcp: returned argument count
+ *
+ * Returns: an array of pointers to strings which are split out from
+ * @str.  This is performed by strictly splitting on white-space; no
+ * quote processing is performed.  Multiple whitespace characters are
+ * considered to be a single argument separator.  The returned array
+ * is always NULL-terminated.  Returns NULL on memory allocation
+ * failure.
+ *
+ * The source string at `str' may be undergoing concurrent alteration via
+ * userspace sysctl activity (at least).  The argv_split() implementation
+ * attempts to handle this gracefully by taking a local copy to work on.
+ */
+char **argv_split(gfp_t gfp, const char *str, int *argcp)
+{
+	char *argv_str;
+	bool was_space;
+	char **argv, **argv_ret;
+	int argc;
+
+	argv_str = kstrndup(str, KMALLOC_MAX_SIZE - 1, gfp);
+	if (!argv_str)
+		return NULL;
+
+	argc = count_argc(argv_str);
+	argv = kmalloc_array(argc + 2, sizeof(*argv), gfp);
+	if (!argv) {
+		kfree(argv_str);
+		return NULL;
+	}
+
+	*argv = argv_str;
+	argv_ret = ++argv;
+	for (was_space = true; *argv_str; argv_str++) {
+		if (isspace(*argv_str)) {
+			was_space = true;
+			*argv_str = 0;
+		} else if (was_space) {
+			was_space = false;
+			*argv++ = argv_str;
+		}
+	}
+	*argv = NULL;
+
+	if (argcp)
+		*argcp = argc;
+	return argv_ret;
+}
+EXPORT_SYMBOL(argv_split);