test: avoid interface_ipc.py race and null pointer dereference

ryanofsky commented at 7:26 pm on March 2, 2026: contributor

Avoid race condition in run_deprecated_mining_test caused by creating and immediately destroying an unused worker thread. This is leading to test failures reported by maflcko in #34711

Avoid race condition in run_deprecated_mining_test caused by creating and
immediately destroying an unused worker thread. This leads to test failures
reported by maflcko in #34711

1c1de334e9

DrahtBot added the label Tests on Mar 2, 2026

DrahtBot commented at 7:26 pm on March 2, 2026: contributor

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Type	Reviewers
ACK	w0xlt, optout21, l0rinc, enirox001

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achow101 added this to the milestone 31.0 on Mar 2, 2026

fanquake commented at 9:42 am on March 3, 2026: member

cc @Sjors

w0xlt commented at 6:49 pm on March 3, 2026: contributor

ACK 1c1de334e9c0e3b4c72c3f3fe45b1f4df5ce4502 In run_deprecated_mining_test, ctx was created but never passed to any call, causing the race condition. The only call is init.makeMiningOld2() which takes no arguments.

in test/functional/interface_ipc.py:76 in 1c1de334e9

70@@ -71,7 +71,9 @@ async def async_routine():
71     def run_deprecated_mining_test(self):
72         self.log.info("Running deprecated mining interface test")
73         async def async_routine():
74-            ctx, init = await make_capnp_init_ctx(self)
75+            node = self.nodes[0]
76+            connection = await capnp.AsyncIoStream.create_unix_connection(node.ipc_socket_path)
77+            init = capnp.TwoPartyClient(connection).bootstrap().cast_as(self.capnp_modules['init'].Init)

optout21 commented at 10:57 am on March 4, 2026:

To reduce code duplication, this could be solved by breaking up make_capnp_init_ctx into two: one to create init only, and the other also the ctx. Counter arguments:

this is a quick test fix
this is the single place where ctx is not needed.

Feel free to resolve this comment if discarded.

optout21 commented at 11:14 am on March 4, 2026: contributor

utACK 1c1de334e9c0e3b4c72c3f3fe45b1f4df5ce4502

This is a fix for an identified sporadic CI failure, due to a race condition, due to a quick create-and-destroy of a capnp context. The change is test-only and limited. Instead of calling into the make_capnp_init_ctx util, only its needed part is inlined. Verified by code review and unit tests.

l0rinc commented at 12:46 pm on March 4, 2026: contributor

Tested ACK 1c1de334e9c0e3b4c72c3f3fe45b1f4df5ce4502

Added a temporary delay to ProxyServer::makeThread to make the race explicit. It passes after the fix and fails before it.

 0diff --git a/src/ipc/libmultiprocess/src/mp/proxy.cpp b/src/ipc/libmultiprocess/src/mp/proxy.cpp
 1--- a/src/ipc/libmultiprocess/src/mp/proxy.cpp	(revision 9cad97f6cdf1bd660732cd10e844a6a7e0771ea0)
 2+++ b/src/ipc/libmultiprocess/src/mp/proxy.cpp	(revision 79e9c9cc5be4932352116e6db0ea84f5f769929c)
 3@@ -413,6 +413,7 @@
 4         g_thread_context.thread_name = ThreadName(m_connection.m_loop->m_exe_name) + " (from " + from + ")";
 5         g_thread_context.waiter = std::make_unique<Waiter>();
 6         thread_context.set_value(&g_thread_context);
 7+        usleep(250000); // TODO Reproducer-only delay to widen the race between thread startup and shutdown.
 8         Lock lock(g_thread_context.waiter->m_mutex);
 9         // Wait for shutdown signal from ProxyServer<Thread> destructor (signal
10         // is just waiter getting set to null.)

 0cmake -B build -DCMAKE_BUILD_TYPE=Debug && cmake --build build -j && build/test/functional/test_runner.py interface_ipc.py
 1...
 21/1 - interface_ipc.py failed, Duration: 4 s
 3
 4stdout:
 52026-03-04T12:41:29.808409Z TestFramework (INFO): PRNG seed is: 9184316120798979695
 62026-03-04T12:41:29.808817Z TestFramework (INFO): Initializing test directory /var/folders/5t/04gq0pqj5yv4t8cxw51q0s2m0000gn/T/test_runner_₿_🏃_20260304_124129/interface_ipc_0
 72026-03-04T12:41:33.104595Z TestFramework (INFO): Running echo test
 82026-03-04T12:41:33.361561Z TestFramework (INFO): Running mining test
 92026-03-04T12:41:33.619016Z TestFramework (INFO): Running deprecated mining interface test
102026-03-04T12:41:33.675022Z TestFramework (INFO): Stopping nodes
11[node 0] Cleaning up ipc directory '/var/folders/5t/04gq0pqj5yv4t8cxw51q0s2m0000gn/T/test-ipc-0e6nefup'
12
13
14stderr:
15Traceback (most recent call last):
16  File "/Users/lorinc/IdeaProjects/bitcoin/build/test/functional/interface_ipc.py", line 90, in <module>
17    IPCInterfaceTest(__file__).main()
18    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
19  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_framework.py", line 156, in main
20    exit_code = self.shutdown()
21  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_framework.py", line 289, in shutdown
22    self.stop_nodes()
23    ~~~~~~~~~~~~~~~^^
24  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_framework.py", line 535, in stop_nodes
25    node.wait_until_stopped()
26    ~~~~~~~~~~~~~~~~~~~~~~~^^
27  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_node.py", line 524, in wait_until_stopped
28    self.wait_until(lambda: self.is_node_stopped(**kwargs), timeout=timeout)
29    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
30  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_node.py", line 931, in wait_until
31    return wait_until_helper_internal(test_function, timeout=timeout, timeout_factor=self.timeout_factor, check_interval=check_interval)
32  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/util.py", line 429, in wait_until_helper_internal
33    if predicate():
34       ~~~~~~~~~^^
35  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_node.py", line 524, in <lambda>
36    self.wait_until(lambda: self.is_node_stopped(**kwargs), timeout=timeout)
37                            ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
38  File "/Users/lorinc/IdeaProjects/bitcoin/test/functional/test_framework/test_node.py", line 500, in is_node_stopped
39    assert return_code in expected_ret_code, self._node_msg(
40           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
41AssertionError: [node 0] Node returned unexpected exit code (-11) vs ((0,)) when stopping
42[node 0] Cleaning up leftover process
43
44
45
46TEST             | STATUS    | DURATION
47
48interface_ipc.py | ✖ Failed  | 4 s
49                                                                                                                                                                                                 
50ALL              | ✖ Failed  | 4 s (accumulated)                                                                                                                                                 
51Runtime: 4 s

enirox001 commented at 1:10 pm on March 4, 2026: contributor

ACK 1c1de33

Tested locally on Fedora (-DENABLE_IPC=ON).

To verify the race condition, I artificially widened the race window on master by injecting a 100ms std::this_thread::sleep_for inside ProxyServer::makeThread just before the waiter mutex lock. This successfully forced the fatal crash during the test teardown sequence.

Compiling this PR branch with the exact same sabotaged C++ code results in the test passing. Because the test now bypasses make_capnp_init_ctx and connects directly without requesting a remote worker thread, makeThread is never invoked, completely eliminating the premature teardown race condition.

fanquake merged this on Mar 4, 2026

fanquake closed this on Mar 4, 2026

test: avoid interface_ipc.py race and null pointer dereference #34715

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