Celery Error "Recursive result parents" on some tasks trees

The Fix

pip install celery==5.4.0

Based on closed celery/celery issue #8890 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -1225,6 +1225,12 @@ def prepare_steps(self, args, kwargs, tasks,
                         root_id=root_id, app=app,
                     )
+                if tasks:
+                    prev_task = tasks[-1]
+                    prev_res = results[-1]

repro.py

import celery

celery_app = celery.Celery()
celery_app.config_from_object({
    'broker_url': 'memory://',
    'broker_backend': 'memory://',
    'result_backend': 'cache+memory://'
})


@celery.shared_task
def test_task(x: int):
    print(x)


def main():
    t1 = celery.chain(test_task.s(0), celery.group(test_task.s(1), test_task.s(2)), test_task.s(3) | test_task.s(4))
    t2 = celery.chord([test_task.s(5), test_task.s(6)], t1)
    t3 = celery.chord([test_task.s(7)], t2)
    t3.apply_async()


if __name__ == '__main__':
    main()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install celery==5.4.0\nWhen NOT to use: Do not apply this fix if the task structure does not include groups in the middle.\n\n

Why This Fix Works in Production

Trigger: t3.apply_async()
Mechanism: The issue arises from incorrect handling of task chains that include a group in the middle
Why the fix works: Fixes a bug related to recursive result parents in task chains that include a group in the middle. (first fixed release: 5.4.0).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

The issue arises from incorrect handling of task chains that include a group in the middle
Surfaces as: Traceback (most recent call last):

Proof / Evidence

GitHub issue: #8890
Fix PR: https://github.com/celery/celery/pull/8903
First fixed release: 5.4.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.43

Verified Execution

We executed the runnable minimal repro in a temporary environment and captured exit codes + logs.

Status: PASS
Ran: 2026-02-11T16:52:29Z
Package: celery
Fixed: 5.4.0
Mode: fixed_only
Outcome: ok

Logs

affected (exit=None)

fixed (exit=0)

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“# Checklist  - [x] I have verified that the issue exists against the main branch of Celery. - [ ] This has already been asked to the discussions forum first. - [x] I have read the r”

Issue thread · issue description · source

Failure Signature (Search String)

t3.apply_async()

Error Message

Stack trace

error.txt

Error Message
-------------
Traceback (most recent call last):
  File "scratch.py", line 20, in <module>
    t3.apply_async()
  File "C:\git\celery\celery\canvas.py", line 2152, in apply_async
    return self.run(tasks, body, args, task_id=task_id, kwargs=kwargs, **merged_options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\git\celery\celery\canvas.py", line 2233, in run
    bodyres = body.freeze(task_id, root_id=root_id)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\git\celery\celery\canvas.py", line 2093, in freeze
    raise RuntimeError('Recursive result parents')
RuntimeError: Recursive result parents

Minimal Reproduction

repro.py

import celery

celery_app = celery.Celery()
celery_app.config_from_object({
    'broker_url': 'memory://',
    'broker_backend': 'memory://',
    'result_backend': 'cache+memory://'
})


@celery.shared_task
def test_task(x: int):
    print(x)


def main():
    t1 = celery.chain(test_task.s(0), celery.group(test_task.s(1), test_task.s(2)), test_task.s(3) | test_task.s(4))
    t2 = celery.chord([test_task.s(5), test_task.s(6)], t1)
    t3 = celery.chord([test_task.s(7)], t2)
    t3.apply_async()


if __name__ == '__main__':
    main()

What Broke

Tasks may fail to execute properly, leading to unexpected behavior in task chains.

Why It Broke

The issue arises from incorrect handling of task chains that include a group in the middle

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==5.4.0

When NOT to use: Do not apply this fix if the task structure does not include groups in the middle.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/8903

First fixed release: 5.4.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not apply this fix if the task structure does not include groups in the middle.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
5.4.0	Fixed

Related Issues

No related fixes found.

Cluster: celery:data-consistency Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Duplicates Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

Celery Error "Recursive result parents" on some tasks trees (Fix)