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, 33 insertions, 0 deletions

diff --git a/include/asm-generic/irq_regs.h b/include/asm-generic/irq_regs.h
new file mode 100644
index 000000000..2e7c6e89d
--- /dev/null
+++ b/include/asm-generic/irq_regs.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Fallback per-CPU frame pointer holder
+ *
+ * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _ASM_GENERIC_IRQ_REGS_H
+#define _ASM_GENERIC_IRQ_REGS_H
+
+#include <linux/percpu.h>
+
+/*
+ * Per-cpu current frame pointer - the location of the last exception frame on
+ * the stack
+ */
+DECLARE_PER_CPU(struct pt_regs *, __irq_regs);
+
+static inline struct pt_regs *get_irq_regs(void)
+{
+	return __this_cpu_read(__irq_regs);
+}
+
+static inline struct pt_regs *set_irq_regs(struct pt_regs *new_regs)
+{
+	struct pt_regs *old_regs;
+
+	old_regs = __this_cpu_read(__irq_regs);
+	__this_cpu_write(__irq_regs, new_regs);
+	return old_regs;
+}
+
+#endif /* _ASM_GENERIC_IRQ_REGS_H */