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, 70 insertions, 0 deletions

diff --git a/net/ipv6/protocol.c b/net/ipv6/protocol.c
new file mode 100644
index 000000000..d4b1806ba
--- /dev/null
+++ b/net/ipv6/protocol.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * INET		An implementation of the TCP/IP protocol suite for the LINUX
+ *		operating system.  INET is implemented using the  BSD Socket
+ *		interface as the means of communication with the user level.
+ *
+ *		PF_INET6 protocol dispatch tables.
+ *
+ * Authors:	Pedro Roque	<roque@di.fc.ul.pt>
+ */
+
+/*
+ *      Changes:
+ *
+ *      Vince Laviano (vince@cs.stanford.edu)       16 May 2001
+ *      - Removed unused variable 'inet6_protocol_base'
+ *      - Modified inet6_del_protocol() to correctly maintain copy bit.
+ */
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/spinlock.h>
+#include <net/protocol.h>
+
+#if IS_ENABLED(CONFIG_IPV6)
+struct inet6_protocol __rcu *inet6_protos[MAX_INET_PROTOS] __read_mostly;
+EXPORT_SYMBOL(inet6_protos);
+
+int inet6_add_protocol(const struct inet6_protocol *prot, unsigned char protocol)
+{
+	return !cmpxchg((const struct inet6_protocol **)&inet6_protos[protocol],
+			NULL, prot) ? 0 : -1;
+}
+EXPORT_SYMBOL(inet6_add_protocol);
+
+int inet6_del_protocol(const struct inet6_protocol *prot, unsigned char protocol)
+{
+	int ret;
+
+	ret = (cmpxchg((const struct inet6_protocol **)&inet6_protos[protocol],
+		       prot, NULL) == prot) ? 0 : -1;
+
+	synchronize_net();
+
+	return ret;
+}
+EXPORT_SYMBOL(inet6_del_protocol);
+#endif
+
+const struct net_offload __rcu *inet6_offloads[MAX_INET_PROTOS] __read_mostly;
+EXPORT_SYMBOL(inet6_offloads);
+
+int inet6_add_offload(const struct net_offload *prot, unsigned char protocol)
+{
+	return !cmpxchg((const struct net_offload **)&inet6_offloads[protocol],
+			NULL, prot) ? 0 : -1;
+}
+EXPORT_SYMBOL(inet6_add_offload);
+
+int inet6_del_offload(const struct net_offload *prot, unsigned char protocol)
+{
+	int ret;
+
+	ret = (cmpxchg((const struct net_offload **)&inet6_offloads[protocol],
+		       prot, NULL) == prot) ? 0 : -1;
+
+	synchronize_net();
+
+	return ret;
+}
+EXPORT_SYMBOL(inet6_del_offload);