From 564f9f9c858ce8bc7af47a7b7763c11b1b0a467c Mon Sep 17 00:00:00 2001
From: anematode <timothy.herchen@gmail.com>
Date: Wed, 27 May 2026 07:05:56 +0200
Subject: [PATCH] Fix sloppy L3 cache detection code

Fixes https://github.com/official-stockfish/Stockfish/issues/6857

Many thanks to Andrew for the repro

closes https://github.com/official-stockfish/Stockfish/pull/6858

No functional change
---
 src/numa.h | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/src/numa.h b/src/numa.h
index afd868dd0..bc704dff9 100644
--- a/src/numa.h
+++ b/src/numa.h
@@ -1166,23 +1166,18 @@ class NumaConfig {
 #if defined(__linux__) && !defined(__ANDROID__)
 
         std::set<CpuIndex> seenCpus;
-        auto               nextUnseenCpu = [&seenCpus]() {
-            for (CpuIndex i = 0;; ++i)
-                if (!seenCpus.count(i))
-                    return i;
-        };
 
-        while (true)
+        for (const auto& [next, _] : systemConfig.nodeByCpu)
         {
-            CpuIndex next = nextUnseenCpu();
-            auto     siblingsStr =
+            if (seenCpus.count(next))
+                continue;
+
+            auto siblingsStr =
               read_file_to_string("/sys/devices/system/cpu/cpu" + std::to_string(next)
                                   + "/cache/index3/shared_cpu_list");
 
             if (!siblingsStr.has_value() || siblingsStr->empty())
-            {
-                break;  // we have read all available CPUs
-            }
+                continue;
 
             L3Domain domain;
             for (size_t c : indices_from_shortened_string(*siblingsStr))