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, 100 insertions, 0 deletions

diff --git a/samples/bpf/tracex3.bpf.c b/samples/bpf/tracex3.bpf.c
new file mode 100644
index 000000000..41f37966f
--- /dev/null
+++ b/samples/bpf/tracex3.bpf.c
@@ -0,0 +1,100 @@
+/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include "vmlinux.h"
+#include <linux/version.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct start_key {
+	dev_t dev;
+	u32 _pad;
+	sector_t sector;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__type(key, long);
+	__type(value, u64);
+	__uint(max_entries, 4096);
+} my_map SEC(".maps");
+
+/* from /sys/kernel/tracing/events/block/block_io_start/format */
+SEC("tracepoint/block/block_io_start")
+int bpf_prog1(struct trace_event_raw_block_rq *ctx)
+{
+	u64 val = bpf_ktime_get_ns();
+	struct start_key key = {
+		.dev = ctx->dev,
+		.sector = ctx->sector
+	};
+
+	bpf_map_update_elem(&my_map, &key, &val, BPF_ANY);
+	return 0;
+}
+
+static unsigned int log2l(unsigned long long n)
+{
+#define S(k) if (n >= (1ull << k)) { i += k; n >>= k; }
+	int i = -(n == 0);
+	S(32); S(16); S(8); S(4); S(2); S(1);
+	return i;
+#undef S
+}
+
+#define SLOTS 100
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(key_size, sizeof(u32));
+	__uint(value_size, sizeof(u64));
+	__uint(max_entries, SLOTS);
+} lat_map SEC(".maps");
+
+/* from /sys/kernel/tracing/events/block/block_io_done/format */
+SEC("tracepoint/block/block_io_done")
+int bpf_prog2(struct trace_event_raw_block_rq *ctx)
+{
+	struct start_key key = {
+		.dev = ctx->dev,
+		.sector = ctx->sector
+	};
+
+	u64 *value, l, base;
+	u32 index;
+
+	value = bpf_map_lookup_elem(&my_map, &key);
+	if (!value)
+		return 0;
+
+	u64 cur_time = bpf_ktime_get_ns();
+	u64 delta = cur_time - *value;
+
+	bpf_map_delete_elem(&my_map, &key);
+
+	/* the lines below are computing index = log10(delta)*10
+	 * using integer arithmetic
+	 * index = 29 ~ 1 usec
+	 * index = 59 ~ 1 msec
+	 * index = 89 ~ 1 sec
+	 * index = 99 ~ 10sec or more
+	 * log10(x)*10 = log2(x)*10/log2(10) = log2(x)*3
+	 */
+	l = log2l(delta);
+	base = 1ll << l;
+	index = (l * 64 + (delta - base) * 64 / base) * 3 / 64;
+
+	if (index >= SLOTS)
+		index = SLOTS - 1;
+
+	value = bpf_map_lookup_elem(&lat_map, &index);
+	if (value)
+		*value += 1;
+
+	return 0;
+}
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;