tests: kill zombie IPC child processes after join timeout

When Python 3.12 CI runs, env-vars enables compute-sanitizer with
--target-processes=all, which attaches to every mp.Process child the
tests spawn. On CUDA 12.9.1 the sanitizer analysis of IPC buffer teardown
gets stuck, so child processes never exit. The existing
join(timeout=CHILD_TIMEOUT_SEC) returns but leaves the child alive.

That zombie keeps its IPC handle open. When pytest teardown runs
ipc_memory_resource's mr.close(), it blocks waiting for the handle to
be released — tying up the runner for hours until GitHub Actions
force-cancels the job. This is the exact pattern in issue #2004
(always Python 3.12 + CUDA 12.9.1 local).

Fix: after join(timeout=...), kill any process still alive so the IPC
handle is released before fixture teardown. Tests still fail (exit code
is non-zero or completed is False), just in seconds rather than hours.

Fixes #2004

Author: aryanputta

cuda_core/tests/memory_ipc/test_send_buffers.py

@@ -39,6 +39,13 @@ def test_main(self, ipc_device, nmrs):
 
             # Wait for the child process.
             process.join(timeout=CHILD_TIMEOUT_SEC)
+            if process.is_alive():
+                # Child is stuck (CUDA context teardown can hang under certain
+                # driver/Python combos — see issue #2004). Kill it so the
+                # IPC handle is released and the fixture teardown doesn't
+                # block the runner for hours.
+                process.kill()
+                process.join()
             assert process.exitcode == 0
 
             # Verify that the buffers were modified.
@@ -96,10 +103,20 @@ def test_main(self, ipc_device, ipc_memory_resource):
         proc_c.start()
 
         # Wait for C to signal completion then clean up.
-        event_c.wait(timeout=CHILD_TIMEOUT_SEC)
+        completed = event_c.wait(timeout=CHILD_TIMEOUT_SEC)
         event_b.set()  # b can finish now
         proc_b.join(timeout=CHILD_TIMEOUT_SEC)
         proc_c.join(timeout=CHILD_TIMEOUT_SEC)
+
+        # Kill any processes that are still alive. Without this, a child stuck
+        # in CUDA context teardown (issue #2004: Python 3.12 + CUDA 12.9.1)
+        # holds IPC handles and blocks fixture teardown indefinitely.
+        for p in (proc_b, proc_c):
+            if p.is_alive():
+                p.kill()
+                p.join()
+
+        assert completed, "process C did not complete within timeout"
         assert proc_b.exitcode == 0
         assert proc_c.exitcode == 0