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, 98 insertions, 0 deletions

diff --git a/lib/once.c b/lib/once.c
new file mode 100644
index 000000000..d801bfa94
--- /dev/null
+++ b/lib/once.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/once.h>
+#include <linux/random.h>
+#include <linux/module.h>
+
+struct once_work {
+	struct work_struct work;
+	struct static_key_true *key;
+	struct module *module;
+};
+
+static void once_deferred(struct work_struct *w)
+{
+	struct once_work *work;
+
+	work = container_of(w, struct once_work, work);
+	BUG_ON(!static_key_enabled(work->key));
+	static_branch_disable(work->key);
+	module_put(work->module);
+	kfree(work);
+}
+
+static void once_disable_jump(struct static_key_true *key, struct module *mod)
+{
+	struct once_work *w;
+
+	w = kmalloc_obj(*w, GFP_ATOMIC);
+	if (!w)
+		return;
+
+	INIT_WORK(&w->work, once_deferred);
+	w->key = key;
+	w->module = mod;
+	__module_get(mod);
+	schedule_work(&w->work);
+}
+
+static DEFINE_SPINLOCK(once_lock);
+
+bool __do_once_start(bool *done, unsigned long *flags)
+	__acquires(once_lock)
+{
+	spin_lock_irqsave(&once_lock, *flags);
+	if (*done) {
+		spin_unlock_irqrestore(&once_lock, *flags);
+		/* Keep sparse happy by restoring an even lock count on
+		 * this lock. In case we return here, we don't call into
+		 * __do_once_done but return early in the DO_ONCE() macro.
+		 */
+		__acquire(once_lock);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(__do_once_start);
+
+void __do_once_done(bool *done, struct static_key_true *once_key,
+		    unsigned long *flags, struct module *mod)
+	__releases(once_lock)
+{
+	*done = true;
+	spin_unlock_irqrestore(&once_lock, *flags);
+	once_disable_jump(once_key, mod);
+}
+EXPORT_SYMBOL(__do_once_done);
+
+static DEFINE_MUTEX(once_mutex);
+
+bool __do_once_sleepable_start(bool *done)
+	__acquires(once_mutex)
+{
+	mutex_lock(&once_mutex);
+	if (*done) {
+		mutex_unlock(&once_mutex);
+		/* Keep sparse happy by restoring an even lock count on
+		 * this mutex. In case we return here, we don't call into
+		 * __do_once_done but return early in the DO_ONCE_SLEEPABLE() macro.
+		 */
+		__acquire(once_mutex);
+		return false;
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(__do_once_sleepable_start);
+
+void __do_once_sleepable_done(bool *done, struct static_key_true *once_key,
+			 struct module *mod)
+	__releases(once_mutex)
+{
+	*done = true;
+	mutex_unlock(&once_mutex);
+	static_branch_disable(once_key);
+}
+EXPORT_SYMBOL(__do_once_sleepable_done);