From 724e7698dc2795cf96f07ba16a078abd4e93cb46 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Sun, 26 Jul 2026 23:44:11 +0200
Subject: kapi/bus: extend stress tests

---
 kernel/kapi/devices/bus.stress.cpp | 81 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 79 insertions(+), 2 deletions(-)

(limited to 'kernel/kapi')

diff --git a/kernel/kapi/devices/bus.stress.cpp b/kernel/kapi/devices/bus.stress.cpp
index 3fefc892..507650f0 100644
--- a/kernel/kapi/devices/bus.stress.cpp
+++ b/kernel/kapi/devices/bus.stress.cpp
@@ -7,6 +7,7 @@
 
 #include <atomic>
 #include <cstddef>
+#include <mutex>
 #include <thread>
 #include <tuple>
 #include <vector>
@@ -21,8 +22,8 @@ namespace
 
 }  // namespace
 
-constexpr auto thread_count = 8;
-constexpr auto devices_per_thread = 200;
+constexpr auto thread_count = 8uz;
+constexpr auto devices_per_thread = 200uz;
 
 SCENARIO("Concurrent attach/detach/lookup on a bus is race-free")
 {
@@ -73,4 +74,80 @@ SCENARIO("Concurrent attach/detach/lookup on a bus is race-free")
       }
     }
   }
+}
+
+SCENARIO("Concurrent removal of a bus with its own children is race-free")
+{
+  GIVEN("A shared parent bus, and a pool of child busses attached to it")
+  {
+    auto parent_bus = kstd::make_shared<kapi::devices::bus>("stress_test_nested_parent");
+    kapi::devices::get_root_bus()->add_child(parent_bus);
+
+    constexpr auto pool_size = 8uz;
+
+    auto pool_lock = std::mutex{};
+    auto pool = std::vector<kstd::shared_ptr<kapi::devices::bus>>{};
+
+    for (auto i = 0uz; i < pool_size; ++i)
+    {
+      auto child = kstd::make_shared<kapi::devices::bus>(kstd::format("stress_test_nested_child_{}", i));
+      parent_bus->add_child(child);
+      pool.push_back(child);
+    }
+
+    WHEN("threads concurrently attach devices to shared child busses, while others tear an entire child bus down "
+         "through the parent and replace it")
+    {
+      auto threads = std::vector<std::jthread>{};
+      threads.reserve(thread_count);
+
+      auto failures = std::atomic<std::size_t>{0};
+
+      for (auto thread_index = 0uz; thread_index < thread_count; ++thread_index)
+      {
+        threads.emplace_back([&pool, &pool_lock, &parent_bus, &failures, thread_index] {
+          for (auto i = 0uz; i < devices_per_thread; ++i)
+          {
+            auto pool_index = (thread_index + i) % pool_size;
+
+            auto child_bus = kstd::shared_ptr<kapi::devices::bus>{};
+            {
+              auto guard = std::lock_guard{pool_lock};
+              child_bus = pool[pool_index];
+            }
+
+            auto name = kstd::format("stress_test_nested_device_{}_{}", thread_index, i);
+            auto device = kstd::make_shared<test_device>(name);
+
+            child_bus->add_child(device);
+
+            if (!child_bus->remove_child(*device))
+            {
+              ++failures;
+            }
+
+            if (i % 25 == 0)
+            {
+              if (parent_bus->remove_child(*child_bus))
+              {
+                auto replacement =
+                    kstd::make_shared<kapi::devices::bus>(kstd::format("stress_test_nested_child_{}", pool_index));
+                parent_bus->add_child(replacement);
+
+                auto guard = std::lock_guard{pool_lock};
+                pool[pool_index] = replacement;
+              }
+            }
+          }
+        });
+      }
+
+      threads.clear();
+
+      THEN("every direct attach to a child bus was matched by a successful removal")
+      {
+        REQUIRE(failures == 0);
+      }
+    }
+  }
 }
\ No newline at end of file
-- 
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