tentacle: cephadm/tests: pre-import tracemalloc to avoid pyfakefs setup race

release-management/backports/01a177f4-63f1-7e3d-a389-f72fcfbb888d.md

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+---
+id: 01a177f4-63f1-7e3d-a389-f72fcfbb888d
+title: 'tentacle: cephadm/tests: pre-import tracemalloc to avoid pyfakefs setup race'
+component: build
+category: fix
+provenance:
+  type: upstream_pr
+  upstream_prs:
+  - https://github.com/ceph/ceph/pull/71189
+  - https://github.com/ceph/ceph/pull/71163
+  upstream_pr_state: merged-main
+  upstream_commits:
+  - 44eff9c1937ea71ac3cd272b08c9dc16660aff10
+  - 79898177cb5f13da1631bb7e22f41248beeb54dc
+  upstream_trackers:
+  - https://tracker.ceph.com/issues/79677
+justification:
+  type: engineering
+  refs:
+  - cobaltcore-dev/cloud-storage#627
+  - ceph/ceph#71189
+  - ceph/ceph#71163
+  - https://tracker.ceph.com/issues/79677
+risk:
+  # Stage-B — fill these during PR prep. See release-management/backports/RISK-RUBRIC.md.
+  blast: cosmetic
+  conflict: clean
+  coverage: weak
+---
+
+## Justification (public)
+
+Fixes an intermittent failure in the cephadm unit test suite that caused
+`make check` to fail spuriously. No runtime behaviour changes.
+
+## Justification (internal)
+
+`run_tox_cephadm` fails on ~25% of arm64 and ~8% of x86 `make check` runs with
+`RuntimeError: dictionary changed size during iteration` in pyfakefs
+`Patcher._find_modules`, followed by ~80 cascading
+`'NoneType' object has no attribute 'add_real_directory'` errors (the Patcher
+is a ref-counted singleton, so a failed `setUp()` never gets its `tearDown()`).
+
+Root cause: pytest >= 8.4's unraisable-exception hook lazily imports
+`tracemalloc` from inside a GC pass triggered by leaked `NamedTemporaryFile`
+finalizers left on the fake filesystem; that mutates `sys.modules` while
+pyfakefs 5.3.5 iterates it. pyfakefs >= 5.10 snapshots with `dict.copy()` and
+is immune, but is not a drop-in upgrade here. Fix pre-imports `tracemalloc` in
+conftest — one line, no production code touched.
+
+We carry the same pyfakefs 5.3.5 pin and unpinned pytest, so we are equally
+exposed; without this, CI noise on the release branch is indistinguishable from
+real regressions.
+
+Upstream state, checked 2026-10-26: #71163 is merged into `main` as
+78193dc918711dee7ecb17f8f206659a3cbaa624. #71189 is its tentacle backport,
+approved and labelled `releng-audit-pass`, but not yet merged.
+
+## Risk notes
+
+(Stage-B rationale: blast / conflict / coverage. Filled during PR prep.)
+
+## Behavior change
+
+(What changes for users? Empty if pure internal fix.)
+
+## Upgrade notes
+
+(Operator instructions, if any.)

src/cephadm/tests/conftest.py

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+# Pre-import tracemalloc so that pytest's unraisable-exception hook
+# (_pytest.unraisableexception.unraisable_hook -> tracemalloc_message) does not
+# lazily import it from inside a garbage-collection pass.
+#
+# Some tests (e.g. TestBootstrap) leave NamedTemporaryFile objects created on
+# the pyfakefs fake filesystem to be garbage collected after the fake fs has
+# been torn down; their __del__ raises, pytest's hook runs during GC and, the
+# first time, imports tracemalloc.  If that GC happens while pyfakefs'
+# Patcher._find_modules() is iterating sys.modules, the `fs` fixture setup
+# fails with "RuntimeError: dictionary changed size during iteration" and,
+# because Patcher is a ref-counted singleton, every later fs-based test errors
+# with "'NoneType' object has no attribute 'add_real_directory'".
+import tracemalloc  # noqa: F401