[KowalskiThomas]

Description

This is an attempt to fix a customer-reported crash (Jira).

• The customer is using a version that already includes this ContextVar-related crash: fix(internal): crash in ContextVar #17407
• It's likely gh-148891: prevent crash in HAMT python/cpython#148928 would fix the crash as well but (1) it would only land in recent versions of CPython -- the customer is using 3.11 -- and (2) I don't have a review/approval yet.

This fix addresses the issue in a sort of makeshift way like the CPython upstream fix would. Since we can't bump reference counts directly from CPython, the PR adds a Rust helper which takes care of it. Not great, not terrible.

Note the bug only happens in versions prior to 3.12 (which made significant changes to the GC and doesn't trigger that HAMT crash anymore), so the fix is gated to them.

---

The crash signature is

Error UnixSignal: Process terminated with SEGV_MAPERR (SIGSEGV)
#0   0x00000000006a3e3b  
#1   0x0000000000690b5b  
#2   0x00000000004a5e01  
#3   0x0000000000690a27  
#4   0x0000000000690990  
#5   0x0000000000690699 PyContextVar_Set 
#6   0x0000000000540be3 _PyEval_EvalFrameDefault 
#7   0x0000000000585937  
#8   0x000000000058512e  
#9   0x000000000054aea5 PyObject_Vectorcall 
#10  0x000000000053d7a6 _PyEval_EvalFrameDefault 
#11  0x0000000000585040  
#12  0x0000000000541c19 _PyEval_EvalFrameDefault 
#13  0x0000000000583177  
#14  0x0000000000581a14  
#15  0x00000000005b418d  
#16  0x000000000053fb96 _PyEval_EvalFrameDefault 
#17  0x00000000005afd4e  
#18  0x00000000005bf334  
#19  0x000000000053f6b2 _PyEval_EvalFrameDefault 
#20  0x0000000000585937  
#21  0x000000000058512e  
#22  0x0000000000570534 PyObject_Call 
#23  0x0000000000541c19 _PyEval_EvalFrameDefault 
#24  0x0000000000565f43 _PyFunction_Vectorcall 
#25  0x00000000005341e9 _PyObject_FastCallDictTstate 
#26  0x000000000056e0f9 _PyObject_Call_Prepend 
#27  0x000000000065a02b  
#28  0x000000000052f59c _PyObject_MakeTpCall 
#29  0x000000000053d7a6 _PyEval_EvalFrameDefault 
#30  0x00000000006140f4  
#31  0x0000000000613757 PyEval_EvalCode 
#32  0x00000000006344eb  
#33  0x0000000000630744  
#34  0x0000000000644be5  
#35  0x00000000006441f4 _PyRun_SimpleFileObject 
#36  0x0000000000644007 _PyRun_AnyFileObject 
#37  0x000000000063ed19 Py_RunMain 
#38  0x00000000006049cd Py_BytesMain 
#39  0x00007f3bd11a6d90 __libc_start_call_main (sysdeps/nptl/libc_start_call_main.h:58)
#40  0x0000000000000000 call_init (csu/libc-start.c:128)
#41  0x00007f3bd11a6e40 call_init (csu/libc-start.c:128)
#42  0x00007f3bd11a6e40 __libc_start_main_alias_2 (csu/libc-start.c:379)
#43  0x0000000000604855 _start 

[datadog-prod-us1-5]

 

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 8 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-py | build linux serverless: [amd64, cp315-cp315, v113741238-d2b8243-manylinux2014_x86_64, 1]     

DataDog/apm-reliability/dd-trace-py | build linux serverless: [amd64, cp315-cp315, v113741491-d2b8243-musllinux_1_2_x86_64, 1]     

DataDog/apm-reliability/dd-trace-py | build linux serverless: [arm64, cp315-cp315, v113741357-d2b8243-manylinux2014_aarch64, 1]     

View all 8 failed jobs.

ℹ️ Info

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🧪 All tests passed
❄️ No new flaky tests detected

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[cit-pr-commenter-54b7da]

Codeowners resolved as

ddtrace/_trace/provider.py                                              @DataDog/apm-sdk-capabilities-python
ddtrace/internal/native/_native.pyi                                     @DataDog/apm-core-python
releasenotes/notes/internal-add-contextvar-helper-d73542f1c6cfceac.yaml  @DataDog/apm-python
src/native/contextvar.rs                                                @DataDog/apm-core-python
src/native/lib.rs                                                       @DataDog/apm-core-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-06-23 14:33:06

Comparing candidate commit e0b4bb5 in PR branch kowalski/fix-fancy-rust-fix-for-hamt-crash with baseline commit 17ff831 in branch main.

Found 0 performance improvements and 5 performance regressions! Performance is the same for 613 metrics, 10 unstable metrics.

scenario:iastaspects-ljust_aspect

• 🟥 execution_time [+62.747µs; +74.169µs] or [+10.674%; +12.617%]

scenario:iastaspects-stringio_noaspect

• 🟥 execution_time [+32.983µs; +39.087µs] or [+8.782%; +10.407%]

scenario:iastaspectsospath-ospathbasename_aspect

• 🟥 execution_time [+89.582µs; +97.860µs] or [+20.414%; +22.301%]

scenario:span-start

• 🟥 execution_time [+1.344ms; +1.491ms] or [+8.736%; +9.694%]

scenario:telemetryaddmetric-1-count-metric-1-times

• 🟥 execution_time [+239.043ns; +272.554ns] or [+11.471%; +13.079%]

[brettlangdon]

small release note nit, but otherwise lgtm

[github-actions]

This change is marked for backport to 4.10, but it conflicts with that branch.
Attempting to cherrypick this change to 4.10 yielded the following error:

Auto-merging ddtrace/internal/native/_native.pyi
CONFLICT (content): Merge conflict in ddtrace/internal/native/_native.pyi
Auto-merging src/native/lib.rs
CONFLICT (content): Merge conflict in src/native/lib.rs
error: could not apply 3886a01b93... Merge e0b4bb5ba265e2480478c810c3dd20b07c8c7f46 into 3776154ce7039bee1c787849df5ac1e09a8f797c

The command used to test backporting was

git fetch origin 4.10 && git checkout origin/4.10 && git checkout -b backport-18599-to-4.10 && git cherry-pick -x --mainline 1 3886a01b931d950846b7e6051182a59cb4a4e3d2

[github-actions]

This change is marked for backport to 4.8, but it conflicts with that branch.
Attempting to cherrypick this change to 4.8 yielded the following error:

Auto-merging ddtrace/internal/native/_native.pyi
CONFLICT (content): Merge conflict in ddtrace/internal/native/_native.pyi
Auto-merging src/native/lib.rs
CONFLICT (content): Merge conflict in src/native/lib.rs
error: could not apply 3886a01b93... Merge e0b4bb5ba265e2480478c810c3dd20b07c8c7f46 into 3776154ce7039bee1c787849df5ac1e09a8f797c

The command used to test backporting was

git fetch origin 4.8 && git checkout origin/4.8 && git checkout -b backport-18599-to-4.8 && git cherry-pick -x --mainline 1 3886a01b931d950846b7e6051182a59cb4a4e3d2

[github-actions]

This change is marked for backport to 4.11, but it conflicts with that branch.
Attempting to cherrypick this change to 4.11 yielded the following error:

Auto-merging ddtrace/internal/native/_native.pyi
CONFLICT (content): Merge conflict in ddtrace/internal/native/_native.pyi
Auto-merging src/native/lib.rs
error: could not apply 3886a01b93... Merge e0b4bb5ba265e2480478c810c3dd20b07c8c7f46 into 3776154ce7039bee1c787849df5ac1e09a8f797c

The command used to test backporting was

git fetch origin 4.11 && git checkout origin/4.11 && git checkout -b backport-18599-to-4.11 && git cherry-pick -x --mainline 1 3886a01b931d950846b7e6051182a59cb4a4e3d2

[github-actions]

This change is marked for backport to 4.9, but it conflicts with that branch.
Attempting to cherrypick this change to 4.9 yielded the following error:

Auto-merging ddtrace/internal/native/_native.pyi
CONFLICT (content): Merge conflict in ddtrace/internal/native/_native.pyi
Auto-merging src/native/lib.rs
CONFLICT (content): Merge conflict in src/native/lib.rs
error: could not apply 3886a01b93... Merge e0b4bb5ba265e2480478c810c3dd20b07c8c7f46 into 3776154ce7039bee1c787849df5ac1e09a8f797c

The command used to test backporting was

git fetch origin 4.9 && git checkout origin/4.9 && git checkout -b backport-18599-to-4.9 && git cherry-pick -x --mainline 1 3886a01b931d950846b7e6051182a59cb4a4e3d2