redis-check-rdb likely remains stuck in a busy-poll loop. The diagnosis was captured, but the patch proposal did not complete cleanly.
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.
Validation expectation: try the project-level build/test entrypoint from the workspace root before reporting only a focused leaf compile. Detected candidate(s): `make` and, if available, `make check`. If the project-level command fails because dependencies or generated files are missing, include the exact command and failure reason in `## Validation`, then run the narrowest relevant compile/test that is still reproducible from a clean checkout.
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. For public upstream review, prepare the final patch against the upstream default integration branch, usually `master` or `main`; use installed or stable source trees for reproduction/backport validation, not as the default merge-request base unless the contribution docs explicitly say to target a stable branch. 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, branch-base choice, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `redis` 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.
A previous Fixer patch attempt already exists for this issue. It was generated by Fixer `0.150.0`. Review that patch before changing code, improve it instead of starting blind, and clean up anything awkward or underexplained. In particular, remove avoidable `goto`, tighten the explanation of what the patch is doing, and make the resulting diff feel ready for upstream git review.
- Prior patch: `./prior-best.patch`
- Prior published session: `./prior-best-session.md`
Validation expectation: try the project-level build/test entrypoint from the workspace root before reporting only a focused leaf compile. Detected candidate(s): `make` and, if available, `make check`. If the project-level command fails because dependencies or generated files are missing, include the exact command and failure reason in `## Validation`, then run the narrowest relevant compile/test that is still reproducible from a clean checkout.
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. For public upstream review, prepare the final patch against the upstream default integration branch, usually `master` or `main`; use installed or stable source trees for reproduction/backport validation, not as the default merge-request base unless the contribution docs explicitly say to target a stable branch. 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, branch-base choice, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `redis` 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. The workspace currently changes these repo-relative paths: src/zmalloc.c. Verify that `## Git Add Paths` matches this exact set and that `## Issue Connection` explains every shipped functional file.
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. For public upstream review, prepare the final patch against the upstream default integration branch, usually `master` or `main`; use installed or stable source trees for reproduction/backport validation, not as the default merge-request base unless the contribution docs explicitly say to target a stable branch. 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, branch-base choice, or evidence limit you found, or say that no relevant local helper was found. Treat this as a `redis` upstream patch, not just a Debian-local workaround.
Validation expectation: try the project-level build/test entrypoint from the workspace root before reporting only a focused leaf compile. Detected candidate(s): `make` and, if available, `make check`. If the project-level command fails because dependencies or generated files are missing, include the exact command and failure reason in `## Validation`, then run the narrowest relevant compile/test that is still reproducible from a clean checkout. 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 co
[truncated 277 bytes]
Response
## Plan Pass
## Problem
Fixer observed a Redis process waking on the server cron cadence and repeatedly doing `openat`/`read`/`close` on `/proc/self/stat` after `epoll_wait` timeouts. The evidence names `redis-check-rdb`, but the captured command line and thread name are `redis-server`, so the relevant upstream path is the shared server/zmalloc RSS sampling path: `serverCron()` -> `cronUpdateMemoryStats()` -> `zmalloc_get_rss()` -> `get_proc_stat_ll(24, ...)`.
## Evidence Confidence
observed
## Proposed Subject
`zmalloc: cache the Linux proc stat fd`
## Patch Plan
Update `src/zmalloc.c` under the existing `HAVE_PROC_STAT` Linux/procfs path so `get_proc_stat_ll()` reuses a cached `/proc/self/stat` descriptor and reads from offset 0 with `pread()` instead of reopening the proc file for every RSS sample. Track `getpid()` with the cached fd so forked children do not reuse a descriptor that still points at the parent’s concrete proc stat file, and open with `O_CLOEXEC`.
This should replace/improve the prior Fixer patch in `prior-best.patch`: keep the same narrow fd-cache idea, preserve the existing 100 ms memory-stat sampling cadence, avoid any avoidable `goto`, and keep a short comment for the fork invariant.
Local conventions/helpers found: Redis uses `run_with_period(100)` for cron throttling, `zmalloc_get_rss()`/`get_proc_stat_ll()` for this memory-stat path, and direct low-level procfs `open`/`read`/`fopen` elsewhere. I did not find a more specific local wrapper for procfs reads; `anetCloexec()` exists for fd cleanup patterns, but opening this proc fd with `O_CLOEXEC` is consistent with nearby low-level code. Contribution/build docs found in `CONTRIBUTING.md`, `README.md`, and `tests/README.md`; the workspace is on `master`, matching the expected upstream integration branch.
## Risks
A cached proc fd must be fork-aware, or a child can report the parent’s RSS. The change is Linux-specific and should remain inside `HAVE_PROC_STAT`.
The evidence is profiler/strace-based and the sampled CPU was low, so the maintainer-facing explanation should describe this as a targeted syscall-overhead mitigation, not a confirmed high-CPU busy-loop fix.
## Validation
From the workspace root, first run project-level entrypoints:
`make`
`make check` if present/available.
If project tests are blocked by dependencies, generated files, or port allocation, report the exact command and failure, then run the narrow fallback:
`make -C src redis-server`
Bounded independent signal check after building: run a short local server under strace before/after the change, for example:
`timeout 4s strace -f -e trace=epoll_wait,openat,pread64,read,close -o /tmp/redis-rss.strace ./src/redis-server --port 0 --save "" --appendonly no --protected-mode no`
Use it only as a signal check: before the patch it should show repeated `openat("/proc/self/stat", ...)`; after the patch it should not reopen that file on each RSS sample. If ptrace/strace is blocked, keep confidence at `observed` and report the blocker.
## Patch Pass
Subject: zmalloc: cache the Linux proc stat fd
## Commit Message
Redis samples RSS, the resident set size memory reported by the OS, through `/proc/self/stat` on Linux. Keep a cached proc stat file descriptor and read it with `pread()` so the periodic memory sampler does not reopen the same proc file on every server cron tick.
The cached descriptor is reopened after fork, because an inherited fd refers to the parent process’ concrete `/proc/<pid>/stat` file.
## Evidence Confidence
observed
## Issue Connection
Fixer observed a sleeping Redis process repeatedly returning from `epoll_wait` and then doing `openat`, `read`, and `close` on `/proc/self/stat` about every 100 ms. This failure signal was observed by Fixer and not independently reproduced.
The code-level cause is the Linux RSS helper path: `serverCron()` calls `cronUpdateMemoryStats()`, which calls `zmalloc_get_rss()`, which used `get_proc_stat_ll()` to open and close `/proc/self/stat` for each sample. I changed `get_proc_stat_ll()` to use a small cached fd opened with `O_CLOEXEC`, read via `pread()`, and reopened when `getpid()` changes after fork. I added a short source comment explaining that fork invariant.
This follows the prior Fixer patch’s narrow approach while keeping Redis’ existing 100 ms memory-stat sampling cadence and avoiding awkward control flow. The expected effect is to remove repeated `/proc/self/stat` open/close churn while keeping RSS samples updated as before. I found no Redis-specific procfs read wrapper; the change stays in the existing `zmalloc_get_rss()`/`get_proc_stat_ll()` helper path. The patch is against the workspace `master` branch.
## Git Add Paths
src/zmalloc.c
## Validation
`make` from the workspace root: passed. It printed a non-fatal dependency clean message from jemalloc, `make[4]: *** tests: No such file or directory. Stop.`, then continued and completed successfully.
`make check` from the workspace root: failed before running tests because the harness could not allocate local ports: `Can't find a non busy port in the 21079-21110 range.`
Focused fallback: `make -C src redis-server` passed; target was up to date after the full build.
Additional checks: `git diff --check` passed, and `./src/redis-server --version` ran successfully.
Independent signal check attempted: `timeout 4s strace -f -e trace=epoll_wait,openat,pread64,read,close -o /tmp/redis-rss-after.strace ./src/redis-server --port 0 --save "" --appendonly no --daemonize no --protected-mode no` failed due sandbox ptrace restrictions: `PTRACE_TRACEME: Operation not permitted` and `ptrace(PTRACE_SEIZE, 5): Operation not permitted`. Confidence remains `observed`, not `reproduced`.
## Review Pass 1
RESULT: ok
The changed path set is exactly `src/zmalloc.c`, and `## Git Add Paths` matches it.
The patch is narrowly scoped to Redis’ existing Linux RSS path, `zmalloc_get_rss()` / `get_proc_stat_ll()`, and the explanation ties the Fixer evidence to the code path: `serverCron()` samples RSS every 100 ms, which previously reopened `/proc/self/stat` for each sample. The response correctly keeps confidence at `observed`, says the signal was not independently reproduced, and frames the change as a targeted syscall-overhead mitigation rather than a confirmed high-CPU bug.
I did not find a more specific Redis procfs wrapper that should replace the direct `open`/`pread` usage here. The fork-aware cached-fd comment explains the non-obvious invariant, and there is no avoidable `goto` or broad behavioral change.
Validation is acceptable: root `make` was run and passed, `make check` was attempted and failed with the exact Redis harness port-allocation blocker, a focused `make -C src redis-server` fallback passed, and the strace reproduction attempt was reported as blocked by ptrace restrictions.
## Workflow Note
Security-sensitive source patches touching authentication, authorization, credentials, cryptography, sandboxing, permissions, or timing/throttling behavior must not be marked pull-request-ready from observed-only or inferred evidence. Reproduce the behavior and include security-impact analysis, or publish a no-patch diagnosis/report for human review.
Diff
diff --git a/src/zmalloc.c b/src/zmalloc.c
index 7d9fe6e..5601279 100644
--- a/src/zmalloc.c
+++ b/src/zmalloc.c
@@ -636,21 +636,47 @@ void zmadvise_dontneed(void *ptr) {
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
+
+static int proc_stat_fd = -1;
+static pid_t proc_stat_pid = -1;
+
+static void close_proc_stat_fd(void) {
+ if (proc_stat_fd != -1) close(proc_stat_fd);
+ proc_stat_fd = -1;
+ proc_stat_pid = -1;
+}
+
+static int get_proc_stat_fd(void) {
+ pid_t pid = getpid();
+
+ /* The fd refers to a concrete /proc/<pid>/stat file, so a forked child
+ * must not reuse the parent's cached descriptor. */
+ if (proc_stat_fd != -1 && proc_stat_pid != pid) close_proc_stat_fd();
+ if (proc_stat_fd == -1) {
+ proc_stat_fd = open("/proc/self/stat", O_RDONLY | O_CLOEXEC);
+ if (proc_stat_fd != -1) proc_stat_pid = pid;
+ }
+ return proc_stat_fd;
+}
#endif
/* Get the i'th field from "/proc/self/stat" note i is 1 based as appears in the 'proc' man page */
int get_proc_stat_ll(int i, long long *res) {
#if defined(HAVE_PROC_STAT)
char buf[4096];
- int fd, l;
+ ssize_t l = -1;
char *p, *x;
- if ((fd = open("/proc/self/stat",O_RDONLY)) == -1) return 0;
- if ((l = read(fd,buf,sizeof(buf)-1)) <= 0) {
- close(fd);
- return 0;
+ for (int attempts = 0; attempts < 2; attempts++) {
+ int fd = get_proc_stat_fd();
+ if (fd == -1) return 0;
+
+ l = pread(fd,buf,sizeof(buf)-1,0);
+ if (l > 0) break;
+
+ close_proc_stat_fd();
}
- close(fd);
+ if (l <= 0) return 0;
buf[l] = '\0';
if (buf[l-1] == '\n') buf[l-1] = '\0';