---
id: "bug-1828"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "scheduler"
severity: "unknown"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 1
files: ["src/scheduler/src/plugins/limit.c (match_job_host_limit_)", "src/scheduler/testsuite/test_repl_limit_table.c (new test)"]
tags: ["scheduler", "limit-plugin", "kvmgr", "error-code-convention", "not-found-vs-error", "match_job_host_limit_", "sibling-of-bug-1786", "scheduler-sim-live-allocation", "task-2.3"]
related: []
legacy: true
---

# bug-1828: IMPACT CORRECTED 2026-09-18 (independent review of scheduler-sim-live-allocation task 2.3): this…

## Description
IMPACT CORRECTED 2026-09-18 (independent review of scheduler-sim-live-allocation task 2.3): this is NOT just a display/accounting gap -- it meant host-scoped resource limits were NEVER ACTUALLY ENFORCED, in ANY mode (normal or simulation), for this function's entire history. Originally discovered while writing scheduler-sim-live-allocation spec task 2.3's own required TDD test (a host-scoped limit match, via the simulation-mode-registered limit plugin, must create a real usage instance verifiable through limit_get_usage_instances()). limit_prepare_allocation()/match_job_host_limit_() consistently returned rc=-2 (-ENOENT) instead of >= 0, and no usage instance was ever created, even though match_limit() itself genuinely matched (rc=1) and is_host_based_limit() correctly identified the limit as host-based. Tracing the call chain (plugin.c's plugin_prepare_allocation() hook loop -> sched_fill_limit_requests()) shows the missing usage instance meant a host-scoped limit's vres was never added to obj->hlimits, so sched_fill_limit_requests() always iterated an empty list -- the limit's numeric cap was silently never applied to any job's resource request, in production, since this code existed. This does not corrupt the dispatch/pend decision machinery itself (plugin_prepare_allocation()'s hook-calling loop discards the hook's return value, so the bug never fed into a control-flow branch) -- it is a dormant-limit-never-binds defect, but a real enforcement gap, not merely a cosmetic one.

## Environment
_Not recorded (migrated from buglog.json)._

## Reproduction
_Not recorded (migrated from buglog.json)._

## Root cause
match_job_host_limit_() (src/scheduler/src/plugins/limit.c) is the host-scoped sibling of match_job_global_limit_() and has the same defect CLASS bug-1786 fixed in that function alone (misinterpreting key_find()'s negative "not found" return as fatal, rather than the correct not-yet-instantiated signal) -- not byte-for-byte identical wording (bug-1786's own guard was `if (rc <= 0) { return rc; }`; this sibling's was `if (rc < 0) { return rc; }`), same underlying mistake. Right after a successful match_limit(), it does `rc = key_find(privdata->instances, vresname, &vres); if (rc < 0) { return rc; }` before the `if (vres == NULL) { instantiate_limit(...) }` block below it. On the FIRST-EVER lookup of a given vresname (always true the first time a host-scoped limit ever matches), key_find() signals "not found" as a NEGATIVE rc (-ENOENT), not 0 -- this codebase's established kvmgr convention (get_group(), is_host_based_limit(), and bug-1786/bug-1495's own root causes) -- so this early-return unconditionally caught the expected miss and returned before instantiate_limit() could ever run. bug-1786 (2026-09-07) fixed this exact defect class in match_job_global_limit_() but never touched its host-scoped sibling, which retained the bug because no test exercised match_job_host_limit_()/limit_prepare_allocation() with real matching until this task added one (verified via grep: zero prior test call sites for either function anywhere in the test suite).

## Fix
FIXED (2026-09-18, scheduler-sim-live-allocation task 2.3). Removed the erroneous `if (rc < 0) { return rc; }` guard in match_job_host_limit_() entirely, mirroring match_job_global_limit_()'s own bug-1786 fix exactly: `vres` (calloc'd NULL, only ever reassigned by a successful key_find) is already the correct, sufficient signal for "needs instantiation" via the existing `if (vres == NULL)` block immediately below. TDD: new test test_limit_prepare_allocation_matches_host_limit_via_sim_registered_plugin (test_repl_limit_table.c) drives the real limit_prepare_allocation()/match_job_host_limit_() path against a plugin registered via plugin_register_core() and a real percent-based host-scoped limit; RED (rc=-2, confirmed via temporary debug instrumentation tracing is_host_based_limit()=1, match_limit()=1, but limit_prepare_allocation()=-2) before this fix, GREEN (rc>=0, usage instance created and visible via limit_get_usage_instances()) after. Full scheduler suite: 79/79, zero regressions.

## Verification
_Not recorded (migrated from buglog.json)._

## References
_Not recorded (migrated from buglog.json)._