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, 49 insertions, 0 deletions

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
new file mode 100644
index 000000000..1df60645f
--- /dev/null
+++ b/include/net/dropreason.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _LINUX_DROPREASON_H
+#define _LINUX_DROPREASON_H
+#include <net/dropreason-core.h>
+
+/**
+ * enum skb_drop_reason_subsys - subsystem tag for (extended) drop reasons
+ */
+enum skb_drop_reason_subsys {
+	/** @SKB_DROP_REASON_SUBSYS_CORE: core drop reasons defined above */
+	SKB_DROP_REASON_SUBSYS_CORE,
+
+	/**
+	 * @SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE: mac80211 drop reasons
+	 * for unusable frames, see net/mac80211/drop.h
+	 */
+	SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE,
+
+	/**
+	 * @SKB_DROP_REASON_SUBSYS_OPENVSWITCH: openvswitch drop reasons,
+	 * see net/openvswitch/drop.h
+	 */
+	SKB_DROP_REASON_SUBSYS_OPENVSWITCH,
+
+	/**
+	 * @SKB_DROP_REASON_SUBSYS_QDISC: TC qdisc drop reasons,
+	 * see include/net/dropreason-qdisc.h
+	 */
+	SKB_DROP_REASON_SUBSYS_QDISC,
+
+	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
+	SKB_DROP_REASON_SUBSYS_NUM
+};
+
+struct drop_reason_list {
+	const char * const *reasons;
+	size_t n_reasons;
+};
+
+/* Note: due to dynamic registrations, access must be under RCU */
+extern const struct drop_reason_list __rcu *
+drop_reasons_by_subsys[SKB_DROP_REASON_SUBSYS_NUM];
+
+void drop_reasons_register_subsys(enum skb_drop_reason_subsys subsys,
+				  const struct drop_reason_list *list);
+void drop_reasons_unregister_subsys(enum skb_drop_reason_subsys subsys);
+
+#endif