dockerd likely remains stuck in a socket churn loop. A diagnosis report and patch proposal were created locally.
Published session
Prompt
## Plan Pass
You are planning a fixer patch before any edits happen.
Read the evidence bundle at `./evidence.json`. The prepared workspace is `./workspace` and it was acquired via `debian-source`. The original pre-edit snapshot is available at `./source` if you need to inspect it. For interpreter processes, plan from the script/application entrypoint evidence first and include the runtime only as a second investigation target unless the evidence proves a runtime bug.
Upstream-style expectation: before planning or editing, check for contribution/style docs (`CONTRIBUTING`, `HACKING`, `README-hacking`, `README.md`, `docs/`, `dev-docs/`) and scan the touched subsystem for local helpers. If the project has wrappers for file IO, path-relative IO, process spawning, memory allocation, logging, locking, or platform compatibility, prefer those wrappers over generic libc/std APIs. Do not invent a reproducer or user-visible failure that is not in the evidence bundle; if the evidence is profiler-only or indirect, describe it as a targeted mitigation or stop with a diagnosis instead of presenting a speculative patch as a confirmed bug fix. In the plan and final validation, name any such helper, convention, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `docker.io` upstream patch, not just a Debian-local workaround. Inspect the relevant code, nearby callers, project contribution docs, and local helper/compat APIs, but do not edit files in this pass.
Return a short markdown plan with these exact sections:
## Problem
## Evidence Confidence
## Proposed Subject
## Patch Plan
## Risks
## Validation
Classify `## Evidence Confidence` as exactly one of `reproduced`, `observed`, or `inferred`. Use `inferred` only for a no-patch diagnosis/report plan unless you can name the extra evidence you will collect before editing; inferred source patches are blocked by Fixer because they are not pull-request-ready. For `observed` source-patch plans, plan to say in the final `## Issue Connection` that the failure was observed by Fixer and not independently reproduced. If the plan touches authentication, authorization, credentials, cryptography, sandboxing, permissions, or timing/throttling behavior, treat it as security-sensitive: do not plan a source patch unless validation can reproduce the behavior and analyze the security impact; otherwise plan a no-patch diagnosis/report. The plan must explain how the proposed code change addresses the observed issue evidence, call out any prior Fixer patch that should be improved or replaced, reject awkward control flow such as avoidable `goto` if there is a cleaner bounded alternative, name any local helper APIs or maintainer conventions the patch should follow, and keep the intended maintainer-facing explanation clear enough that someone unfamiliar with the local complaint wording can still follow the fix. In `## Validation`, name the reproducible configure/build/test entrypoint you will try from the workspace root before any focused leaf compile or smoke check, and include one bounded independent reproduction attempt for the collected failure signal when it is safe and cheap. Do not plan to claim `reproduced` unless that reproduction command or test can actually show the failure.
## Patch Pass
You are working on a bounded fixer proposal.
Read the evidence bundle at `./evidence.json`. The prepared workspace is `./workspace` and it was acquired via `debian-source`. Produce the smallest reasonable patch for the target repository, keep the change upstreamable, prefer the clearest control flow available, and do not keep avoidable `goto` when a simpler structure would read better. Before introducing new file, process, allocation, locking, networking, or platform APIs, inspect nearby code and project contribution docs for existing helpers or compatibility wrappers and use those local patterns unless you can explain why they do not fit. Validate from a reproducible workspace-root entrypoint before falling back to focused leaf commands; if a build or test cannot run, report the exact command, the exact blocker, and any narrower check you ran instead. During validation, also try one bounded independent reproduction of the collected failure signal when it is safe and cheap, such as a failing test, smoke command, perf/strace comparison, or before/after runtime check. Only use `reproduced` if that command or test actually reproduced the failure; otherwise keep `observed` and report the reproduction blocker. The final explanation must connect the observed issue evidence to the actual code change, not just paraphrase the diff. Write like a maintainer is going to read the patch mail cold: explain the bug in plain language, define subsystem-specific jargon the first time you need it, and make the causal story obvious. Explicitly classify evidence confidence as `reproduced`, `observed`, or `inferred`: `reproduced` means you reproduced the failure locally; `observed` means Fixer has direct crash/log/trace evidence but you did not independently reproduce it; `inferred` means the source patch is not pull-request-ready, so do not leave a source diff unless you first gather stronger observed/reproduced evidence; otherwise return a no-patch diagnosis/report. For any source-changing `observed` patch, say explicitly in `## Issue Connection` that the failure was observed by Fixer and not independently reproduced. Security-sensitive areas such as authentication, authorization, credentials, cryptography, sandboxing, permissions, and timing/throttling behavior need reproduced evidence plus explicit security-impact analysis before leaving a source diff; otherwise return a no-patch diagnosis/report for human review. If you introduce non-obvious state translation, index remapping, or backend split logic, add a short source comment that explains the invariant being preserved.
Start by explaining the likely root cause from the collected perf, strace, and /proc evidence. If you cannot land a safe patch, leave a diagnosis that is strong enough for an upstream bug report.
Upstream-style expectation: before planning or editing, check for contribution/style docs (`CONTRIBUTING`, `HACKING`, `README-hacking`, `README.md`, `docs/`, `dev-docs/`) and scan the touched subsystem for local helpers. If the project has wrappers for file IO, path-relative IO, process spawning, memory allocation, logging, locking, or platform compatibility, prefer those wrappers over generic libc/std APIs. Do not invent a reproducer or user-visible failure that is not in the evidence bundle; if the evidence is profiler-only or indirect, describe it as a targeted mitigation or stop with a diagnosis instead of presenting a speculative patch as a confirmed bug fix. In the plan and final validation, name any such helper, convention, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `docker.io` upstream patch, not just a Debian-local workaround.
Keep the change narrowly scoped and summarize validation clearly.
In every authoring pass, your final response must start with `Subject: <single-line git commit subject>` and then include these markdown sections exactly:
## Commit Message
A short upstream-friendly explanation of what changed and why. Write it in plain language that a maintainer can follow without local complaint context. If you use subsystem jargon, define it immediately.
## Evidence Confidence
Exactly one word: `reproduced`, `observed`, or `inferred`. Use `reproduced` only when you reproduced the failure locally with a command or test, and include that command/test in `## Validation`. Use `observed` when Fixer has direct crash/log/trace evidence but you did not independently reproduce it. If `## Git Add Paths` lists source files for an `observed` patch, `## Issue Connection` must explicitly say the failure was observed by Fixer and not independently reproduced. Security-sensitive source changes touching authentication, authorization, credentials, cryptography, sandboxing, permissions, or timing/throttling behavior require reproduced evidence and explicit security-impact analysis; otherwise list `None` under `## Git Add Paths` and write a no-patch diagnosis/report. Use `inferred` for profiler/strace/indirect evidence; inferred responses may be no-patch diagnoses or reports, but inferred source patches are not pull-request-ready until stronger evidence is gathered.
## Issue Connection
Write this as maintainer-facing patch mail, not as local Fixer notes. Cover four things explicitly in readable sentences: the user-visible symptom or the exact collected signal, the code-level cause or the cautious inference from evidence, the specific change you made, and the expected effect. Do not invent a reproducer, command line, crash, or user-visible failure that is not present in the evidence bundle. If the evidence is direct-but-not-reproduced, say it was observed by Fixer and not independently reproduced. If the evidence is indirect and you did not gather stronger evidence, do not leave a source diff; write a no-patch diagnosis/report instead. Include an explicit effect sentence such as `The expected effect is ...`, `This should reduce ...`, or `This prevents ...` for source patches. If the logic is non-obvious in code, mention that you added a short explanatory comment.
## Git Add Paths
List the repo-relative paths that belong in the final patch, one per line. Use `None` only when you intentionally made no source changes. Include intentionally new files, and do not list generated build artifacts.
## Validation
List the checks you ran, or say clearly that you could not run them. Include the independent reproduction command/test and result when `## Evidence Confidence` is `reproduced`; if reproduction was attempted but blocked, name the exact blocker and keep confidence at `observed` or `inferred`.
Before editing, read the plan at `./plan-output.txt` and follow it unless the code proves part of it wrong. If you change course, say so explicitly in the final write-up instead of silently drifting from the plan.
## Review Pass 1
You are reviewing a freshly generated fixer patch.
Read the evidence bundle at `./evidence.json`. The prepared workspace is `./workspace` and it was acquired via `debian-source`. Review the first patch pass. The original pre-edit snapshot is available at `./source` for diffing.
Upstream-style expectation: before planning or editing, check for contribution/style docs (`CONTRIBUTING`, `HACKING`, `README-hacking`, `README.md`, `docs/`, `dev-docs/`) and scan the touched subsystem for local helpers. If the project has wrappers for file IO, path-relative IO, process spawning, memory allocation, logging, locking, or platform compatibility, prefer those wrappers over generic libc/std APIs. Do not invent a reproducer or user-visible failure that is not in the evidence bundle; if the evidence is profiler-only or indirect, describe it as a targeted mitigation or stop with a diagnosis instead of presenting a speculative patch as a confirmed bug fix. In the plan and final validation, name any such helper, convention, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `docker.io` upstream patch, not just a Debian-local workaround. The latest author response is at `./patch-output.txt`. Inspect the current code and changed paths like a strict code reviewer. Focus on correctness, regressions, maintainability, awkward control flow such as avoidable `goto`, missing validation, weak or non-gittable commit message text, and explanations that fail to connect the observed issue evidence to the code change. Also review the maintainer experience: the patch mail should be easy to accept upstream, the user-visible bug should be explained in plain language, subsystem-specific jargon should be defined when first used, and any non-obvious state translation or index remapping in code should have a short explanatory comment. Reject patches that omit `## Evidence Confidence`, use anything other than `reproduced`, `observed`, or `inferred`, or sound more certain than that evidence level allows. Reject patches that claim `reproduced` unless `## Validation` names the concrete reproduction command or test and its result. Reject source patches in security-sensitive areas such as authentication, authorization, credentials, cryptography, sandboxing, permissions, and timing/throttling behavior unless the author reproduced the behavior and explicitly analyzed the security impact of the change; observed-only evidence should become a diagnosis/report, not a PR-ready source diff. Reject patches that invent a reproducer, command line, crash, or user-visible failure not present in the evidence bundle; indirect profiler or strace evidence may justify a cautious mitigation, but the author must say it is indirect instead of presenting it as a confirmed upstream bug. Reject patches that introduce generic libc/std APIs when nearby code or project docs provide a local compat/helper API for the same job, unless the author explicitly justifies the exception. Reject validation that only reports a leaf object/syntax build when a project-level configure/build/test entrypoint exists and was not attempted; if a full build cannot run, the author must show the exact failed command and blocker.
Do not apply code changes in this pass.
Return a short markdown review report. The first non-empty line must be exactly one of:
RESULT: ok
RESULT: fix-needed
If you choose `RESULT: fix-needed`, add a `## Findings` section with concrete, actionable items.
Response
## Plan Pass
## Problem
Fixer observed `dockerd` running as `/usr/sbin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock` with low CPU, many sleeping threads, futex-heavy snapshots, and a perf hotspot in kernel `mem_cgroup_handle_over_high`. The bundle’s “socket-churn” label is not backed by available raw artifacts here; the JSON strace excerpt mostly shows `futex`, `waitid`, and `epoll_pwait`, and the raw artifact files referenced in the bundle are not present on disk.
## Evidence Confidence
inferred
## Proposed Subject
No source patch yet: report/diagnose the profiler signal as insufficiently tied to a Moby source bug. A pull-request-ready patch would need extra evidence that maps the observed `dockerd` state to a specific daemon code path, such as symbolized Go stacks, goroutine dumps, available raw strace/perf output, or a bounded reproduction showing actual socket churn or runaway retry behavior.
## Patch Plan
- Do not edit source in this pass. The evidence is profiler-only/indirect and points partly at kernel memory-cgroup throttling, not a confirmed `dockerd` bug.
- Keep investigation anchored at the `dockerd` entrypoint first: `engine/cmd/dockerd/docker.go`, `engine/cmd/dockerd/daemon.go`, and `engine/cmd/dockerd/daemon_unix.go`; only treat containerd/runtime code as secondary unless new evidence implicates it.
- If extra evidence later identifies daemon listener or containerd connection churn, follow local conventions already found: `log.G(ctx)` for logging, `github.com/pkg/errors` wrapping, `daemon/listeners.Init` for listener creation, `go-systemd/activation` for `fd://`, and existing `containerd.New` dial/backoff options in `engine/daemon/daemon.go` / `engine/libcontainerd/supervisor`.
- No prior Fixer patch is present in this workspace to replace or improve; `git status` is clean at `Fixer baseline`.
- Avoid speculative timing/throttling changes. If a future fix touches retry delays, cgroup throttling, API listener delays, or security-related daemon access behavior, first reproduce and assess security impact.
- If a real bounded source fix emerges, keep control flow simple with early returns/defer patterns used in this codebase; do not introduce avoidable `goto`.
## Risks
A source patch from the current evidence would likely optimize the wrong layer. The observed kernel `mem_cgroup_handle_over_high` hotspot may reflect host cgroup configuration or pressure rather than Moby behavior, and the stripped backtraces do not identify Go functions. Changing connection retry, listener, or throttling behavior without reproduction could alter daemon startup, containerd recovery, or API exposure semantics.
## Validation
From the workspace root, first try the project entrypoint `cd engine && make test-unit` as the reproducible configured test command before any focused package checks. If later evidence identifies a package, run the relevant focused `go test` after the full entrypoint attempt.
For a bounded independent reproduction attempt before any source patch, run an instrumented local `dockerd` smoke only if safe in the environment, with an isolated root/exec-root and non-production socket, then collect `perf top`/`perf record`, `strace -f -c`, and `SIGQUIT` goroutine stacks while checking whether `mem_cgroup_handle_over_high` or socket churn actually appears. Do not claim reproduction unless that command shows the failure signal.
## Patch Pass
Subject: Diagnose dockerd memcg profile without patch
## Commit Message
No source change is left for this proposal. The collected signal points at kernel memory-cgroup handling, not a confirmed Moby code path: `mem_cgroup_handle_over_high` is the cgroup v2 memory throttling path used when a process exceeds `memory.high`, while the sampled `dockerd` was sleeping with futex-heavy traces and 0.1% CPU.
I followed the saved plan and did not change course. The relevant daemon code already uses local helpers and conventions: `daemon/listeners.Init` for `fd://` socket activation, `log.G(ctx)` for logging, `github.com/pkg/errors` wrapping, and `containerd.New` with local gRPC dial/backoff options for containerd connections.
## Evidence Confidence
inferred
## Issue Connection
The collected signal is a 3-second profiler sample of `/usr/sbin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock` showing 34.73% in kernel `mem_cgroup_handle_over_high`, many sleeping threads, futex waits, and low total CPU. The evidence bundle also labels the loop as “socket-churn,” but the available strace excerpt is dominated by `futex`, `waitid`, and `epoll_pwait`, and the raw investigation files are not present on disk.
The cautious inference is that this is host memory-cgroup pressure or throttling around the daemon, not yet a localized bug in Moby listener, containerd, or retry code. Because the evidence is profiler/strace-indirect and I could not gather stronger observed or reproduced evidence, I made no source change.
The expected effect is no behavior change. This is a no-patch diagnosis suitable for an upstream bug report, with the next useful evidence being symbolized Go stacks or goroutine dumps, raw perf/strace artifacts, and cgroup `memory.high`/`memory.events` data from the affected daemon.
## Git Add Paths
None
## Validation
`cd engine && timeout 120s make test-unit` failed before tests: the build path emitted `Failed to create stream fd: Operation not permitted`, then `ERROR: mkdir /root/.docker: read-only file system`.
Independent reproduction was blocked. I checked `id -u`, `command -v dockerd`, `command -v perf`, `command -v strace`, the raw investigation directory, and `pgrep -a dockerd`; the tools exist and the shell is root, but there was no live `dockerd` process and `/var/lib/fixer/investigations/2026-05-06T10-55-05.762950439+00-00-dockerd-b732bcc6a3ff` is absent. I did not start a new root `dockerd` smoke because it would touch host containerd/cgroup/network state and would not safely reproduce the collected production memcg signal.
`git status --short` and `git diff --stat` are clean.
## Review Pass 1
RESULT: ok
No source changes are present, and the latest author response correctly treats the profiler/strace evidence as `inferred` rather than leaving a speculative patch.
The report includes the required sections, does not claim local reproduction, names the failed project-level validation command and blocker, and explains why an independent runtime reproduction was not safely performed. It also identifies relevant local conventions/helpers (`daemon/listeners.Init`, `log.G(ctx)`, `github.com/pkg/errors`, `containerd.New` dial/backoff options) and keeps the maintainer-facing explanation appropriately cautious for indirect evidence.