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, 68 insertions, 0 deletions

diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h
new file mode 100644
index 000000000..f27d66fdc
--- /dev/null
+++ b/include/asm-generic/cmpxchg-local.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_CMPXCHG_LOCAL_H
+#define __ASM_GENERIC_CMPXCHG_LOCAL_H
+
+#include <linux/types.h>
+#include <linux/irqflags.h>
+
+extern unsigned long wrong_size_cmpxchg(volatile void *ptr)
+	__noreturn;
+
+/*
+ * Generic version of __cmpxchg_local (disables interrupts). Takes an unsigned
+ * long parameter, supporting various types of architectures.
+ */
+static inline unsigned long __generic_cmpxchg_local(volatile void *ptr,
+		unsigned long old, unsigned long new, int size)
+{
+	unsigned long flags, prev;
+
+	/*
+	 * Sanity checking, compile-time.
+	 */
+	if (size == 8 && sizeof(unsigned long) != 8)
+		wrong_size_cmpxchg(ptr);
+
+	raw_local_irq_save(flags);
+	switch (size) {
+	case 1: prev = *(u8 *)ptr;
+		if (prev == (old & 0xffu))
+			*(u8 *)ptr = (new & 0xffu);
+		break;
+	case 2: prev = *(u16 *)ptr;
+		if (prev == (old & 0xffffu))
+			*(u16 *)ptr = (new & 0xffffu);
+		break;
+	case 4: prev = *(u32 *)ptr;
+		if (prev == (old & 0xffffffffu))
+			*(u32 *)ptr = (new & 0xffffffffu);
+		break;
+	case 8: prev = *(u64 *)ptr;
+		if (prev == old)
+			*(u64 *)ptr = (u64)new;
+		break;
+	default:
+		wrong_size_cmpxchg(ptr);
+	}
+	raw_local_irq_restore(flags);
+	return prev;
+}
+
+/*
+ * Generic version of __cmpxchg64_local. Takes an u64 parameter.
+ */
+static inline u64 __generic_cmpxchg64_local(volatile void *ptr,
+		u64 old, u64 new)
+{
+	u64 prev;
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	prev = *(u64 *)ptr;
+	if (prev == old)
+		*(u64 *)ptr = new;
+	raw_local_irq_restore(flags);
+	return prev;
+}
+
+#endif