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fix(scheduler): populate job-wide total want for per-host resources during global phase (bug-1790)

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Closes the gap bug-1789 explicitly carved out: a GLOBAL limit built on a
per-host resource other than "slots" (e.g. a future absolute global mem
cap) needs ctx->alloc_req.host to carry that resource's job-wide total
want during the global phase, but only "slots" ever got that treatment
(via seqjob/parjob_prepare_allocation()'s own unconditional store).

Adds calc_wanted_host_resval_job_totals() (resreq.c), sharing its loop
body with calc_wanted_global_resvals() via a new static helper
parameterized only by which XCE_RESF_GLOBAL direction to match -- it
computes the SAME job-wide-total formulas (PER_TASK: value*nslots, PER_JOB:
value, PER_HOST: value*nhosts) for non-global resources instead of global
ones. seqjob/parjob_prepare_allocation()'s global-phase branch now calls
it into ctx->alloc_req.host alongside the existing calc_wanted_global_
resvals() call into .shared.

Safety was traced, not assumed: plugin_prepare_allocation() only resets
.host at the top of a per-host call, never during the global phase, and
sched_fill_limit_requests() for glimits reads .host later in the SAME
global-phase invocation -- transferring the value into the limit's
permanent .shared record before any later per-host call ever resets
.host. An earlier candidate fix (reusing calc_wanted_host_resvals()
directly) was rejected during design: its PER_HOST formula and, for
parjob, its per-bucket nslots don't give a job-wide total.

New regression tests in test_seqjob_allocator.c/test_parjob_
combinatorial.c prove a non-"slots" per-host resource ("mem") now gets
correctly populated; parjob's test uses maxTasks=3 specifically to prove
the formula uses the job's whole nslots, not a bucket's share.

Full suite (xce-build.sh all asan --incremental): 92/94, both failures
pre-existing and unrelated (bug-1762, bug-1733's already-documented
xcealloc.c leak). Not live-verified -- no limits.yaml entry exercises
this path yet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GLfB5uWRdmx2WiZSFC7Fm7
This commit is contained in:
Rongsong Shen 2026-09-08 02:57:51 +00:00
parent 028d8f6ac7
commit 9caf1424b9
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7 changed files with 265 additions and 8 deletions
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@ -21436,15 +21436,15 @@
"error_message": "OPEN, NOT A CRASH -- known residual gap explicitly carved out of bug-1789's fix, filed for its own tracking per user request. A hypothetical NEW global limit defined on a per-host resource OTHER than \"slots\" (e.g. a future absolute-value global mem cap, as opposed to the existing percent-based host-scoped mem limits in limits.yaml) would silently under-enforce the same way bug-1789's slots limits did, for a different reason than bug-1789's root cause.",
"file": "src/lib/resreq.c",
"root_cause": "bug-1789 fixed sched_fill_limit_requests()'s READ side: it now picks whichever of alloc_req->shared/alloc_req->host to read a limit's underlying resource's want from by checking that resource's own XCE_RESF_GLOBAL flag on vres->res (and separately picks the WRITE destination for the limit's own vres entry by checking vres->vres's flag) -- see resource.c:928-955. That fix only works because alloc_req->host already has SOME value for \"slots\" to read, staged by seqjob_prepare_allocation()/parjob_prepare_allocation() via a separate, unconditional step outside the normal rusages loop, in EVERY phase including the global one. No other per-host resource gets this special treatment. The general population path -- calc_wanted_global_resvals() (src/lib/resreq.c:734) and calc_wanted_host_resvals() (src/lib/resreq.c:793), both called from seqjob_allocator.c/parjob_allocator.c's prepare_allocation hooks -- each unconditionally skip any resource whose XCE_RESF_GLOBAL flag doesn't match their own phase (calc_wanted_global_resvals() line 763: `if ((r->flags & XCE_RESF_GLOBAL) == 0) continue;`; calc_wanted_host_resvals() line 822: `if ((r->flags & XCE_RESF_GLOBAL) != 0) continue;`), and only calc_wanted_global_resvals() runs during the ctx->worker==NULL global phase. So for any per-host resource other than \"slots\", alloc_req->host is simply never populated with a want during the global phase -- sched_fill_limit_requests()'s now-correct read-side dispatch would read a genuine zero from an empty vector, not a population bug on its own side, but the net effect (a global limit on a per-host resource never seeing a nonzero want) is the same silent under-enforcement bug-1789 fixed for slots.",
"fix": "NOT FIXED -- deliberately out of scope, no limit in the current limits.yaml needs it (the two mem-based limits, night_mem_pct/limits2, are both host-scoped, unaffected either way). Suggested direction (per user note, 2026-09-07): apply the SAME flag-based-dispatch pattern bug-1789 already established on the read side to the population/write side too -- i.e. during the global phase, also check each matched global limit's underlying resource's own XCE_RESF_GLOBAL flag (vres->res->flags, the same check sched_fill_limit_requests() already performs) and, for any resource that flag marks non-global, additionally invoke calc_wanted_host_resvals() (or an equivalent per-resource want computation) to populate alloc_req->host for it before sched_fill_limit_requests() reads it -- rather than relying on a resource-specific special case like slots's separate staging step. This is a materially larger change than bug-1789's (touches the allocator plugins' prepare_allocation hooks, not just resource.c) and should get its own TDD cycle if/when a real limit needs it.",
"fix": "FIXED (2026-09-07, follow-up session, user-driven design). Corrected an earlier, wrong candidate fix (calling calc_wanted_host_resvals() during the global phase) identified during design discussion as invalid: that function's PER_HOST formula returns one host's own share (v->value, no multiplier) and, for parjob specifically, its nslots argument is reset PER BUCKET (parjob_allocator.c's parjob_try_plan_(), ctx->nslots = plan->bucket_slots[b], set right before each candidate host is tried) -- neither matches what a GLOBAL limit needs, which is the job-WIDE total, not any one host's/bucket's share.\n\nREAL FIX: added calc_wanted_host_resval_job_totals() (src/lib/resreq.c), a new function for resources NOT flagged XCE_RESF_GLOBAL that computes the JOB-WIDE TOTAL want using the SAME formulas calc_wanted_global_resvals() already uses for GLOBAL resources (PER_TASK: value*nslots, PER_JOB: value, PER_HOST: value*nhosts -- nslots/nhosts being the whole job's totals, set during the global phase, not any bucket's share). Both functions now share a common static helper (calc_wanted_job_total_resvals_()) parameterized only by which flag direction to match, avoiding duplicating the ~30-line loop body. seqjob_prepare_allocation()/parjob_prepare_allocation()'s global-phase branch (ctx->worker == NULL) now calls this new function into ctx->alloc_req.host immediately alongside the existing calc_wanted_global_resvals() call into .shared.\n\nSAFETY, traced precisely rather than assumed: plugin_prepare_allocation() (plugin.c:607-613) resets ONLY .shared at the top of a global-phase call and ONLY .host at the top of a per-host call -- never the other -- so .host is NOT reset when this new write happens. sched_fill_limit_requests() for obj->glimits runs later in that SAME plugin_prepare_allocation() invocation (plugin.c:644-647), reading and transferring the value into the limit's own permanent .shared record BEFORE any later per-host call ever resets .host. The value is therefore fully consumed and irrelevant by the time .host gets correctly wiped and repopulated with real per-host/per-bucket data for the actual capacity check -- two different consumers at two different times, not a conflict, confirmed by reading parjob_allocator.c's own per-bucket reset code directly (not inferred).\n\nTDD: two new regression tests calling seqjob_prepare_allocation()/parjob_prepare_allocation() directly with ctx.worker == NULL and a \"mem\"-named (non-\"slots\", non-global) rusage entry -- test_seqjob_prepare_allocation_global_phase_stores_host_resource_job_total (test_seqjob_allocator.c) and test_parjob_prepare_allocation_global_phase_stores_host_resource_job_total (test_parjob_combinatorial.c, maxTasks=3 specifically to prove the formula uses the job's WHOLE nslots=3, giving 2.0*3=6.0, not any bucket's share). Both assert .shared stays empty (mem correctly excluded, not globally flagged) and .host carries both the new mem entry and the pre-existing unconditional \"slots\" entry. Both PASS standalone with full Unity PASS lines confirmed (not just suite-level OK).\n\nFull `xce-build.sh all asan --incremental`: 92/94 Ok. The 2 failures are both pre-existing and unrelated, confirmed by cross-referencing this exact buglog: test_job_rusage_reconciles_mem_reservation_against_usage (bug-1762) and libxce test's 456-byte/29-allocation leak in test_xcealloc.c's make_alloc()/make_host_alloc() calls (bug-1733's fix note already confirms this exact leak signature -- 456 bytes, 29 allocations -- present byte-for-byte identically via an independent git-stash A/B rebuild in an earlier, unrelated session). No live limits.yaml entry exercises this path yet (both current mem-based limits are host-scoped), so this fix is unit/integration-tested but not live-deployed -- live verification should accompany the first real global limit on a non-slots per-host resource, when one is actually added.",
"tags": [
"scheduler",
"resource-accounting",
"limits",
"global-limit",
"pre-existing",
"out-of-scope",
"severity-low"
"severity-low",
"fixed"
],
"related_bugs": [
"bug-1789"