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Fix a heap overflow in the hbg Graph recording hazard map, and name its task id spaces by Graph membership - #2030
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FaninBuilder had shrunk to four fields and a single method. Two of those fields, count and slots, were copies of payload.fanin_count and payload.fanin_data(), and STEP 6 copied the count back to the payload at the end of every submit. The append logic itself was never a member: it sat outside the struct as append_fanin_or_fail. append_fanin_or_fail now takes the consumer payload's fanin region and its count directly, so the count accumulates in place and the copy-back is gone. mark_seen becomes the free function fanin_mark_seen, and next_fanin_seen_epoch drops its return value now that the epoch it advances to is read from orch.fanin_seen_current_epoch. The region is still resolved once per task, not per producer: it is named by a SelfRelativePtr delta. submit_task_common zeroes payload.fanin_count before the appends. hbg does not zero-fill the shared-memory task table, so that write is this device-read field's init-on-write point, and payload.init() runs after the appends and must leave it alone. graph_submit_outer needs no zeroing because graph_reset_outer_payload already does it. No functional change. Verified with the 119 non-hardware cpput tests, including the submit-poison contract tests that cover every device-read field, plus the host_build_graph scene tests on a2a3sim and a5sim.
The recording's hazard map holds GRAPH_MAX_NODES task chains and indexes them by a producer's low id field directly, but a recorded node was minted in the RING space as `start_local_task_id + node_index`. Any Graph that begins after the run's first GRAPH_MAX_NODES tasks — the ordinary shape for a decode workload — therefore registered its nodes past the last chain and wrote outside `task_entry_heads`. A recorded node now takes a GRAPH_NODE id whose low field is the node index alone, so the key is in range however far into a run the Graph begins. The recording baseline that existed only to tell a node from a pre-Graph task by numeric range is gone: the two now differ by id space, which is decided at the mint rather than derived by subtraction. Two consequences beyond the out-of-bounds write: - A ring id the main thread allocates while a recorder thread runs can no longer land inside a node's index range and be wired as an internal fanin. That misclassification was unreachable in practice but only because of what a body can hold, not by construction. - A node id that escapes its Graph and is later declared as an explicit dependency now trips append_fanin_or_fail's id-space guard instead of resolving to an unrelated task slot and wiring a wrong edge. An over-cap body skips hazard-map registration: its node index has run past the field make_graph_node packs it into, and the Definition is abandoned already. link_entry and remove_from_task carry a debug_assert on the chain index, so a future caller inserting under the wrong id space is caught where it happens rather than corrupting the heap. test_hbg_tensormap's slot-aliasing case rested on a mask hbg does not have — its own inserts ran one chain past the fixture's dimension. It now pins the invariant that holds: a local id is its own chain index, so distinct producers never share a chain.
TaskIdSpace::RING dated from a ring design host_build_graph no longer has — the header's own comment had to apologize for the name, explaining that the high bits mean storage rather than a ring index. And there is no separate "node" concept to name: everything the runtime schedules is a task, and the only question the high bits answer is whether a task belongs to a Graph task or stands on its own. TaskIdSpace::RING -> TaskIdSpace::GLOBAL TaskIdSpace::GRAPH_NODE -> TaskIdSpace::IN_GRAPH make_ring_task -> make_global_task is_ring_task -> is_global_task make_graph_node -> make_in_graph_task GRAPH_NODE_INDEX_BITS -> IN_GRAPH_TASK_INDEX_BITS TaskIdSpace keeps its name: the field holds which id namespace an id belongs to, which is what "space" says, and "type" would collide conceptually with TaskKind. is_global_task gains a comment naming what its callers actually depend on — that the id resolves to a shared-memory task table slot — since the old name carried that by implication and the new one does not. The two fatal messages that named RING now name GLOBAL. They are diagnostic text, not a contract. The deeper node vocabulary is untouched: GraphNodeStorage, GraphNodeDefinition, graph_node_index, GRAPH_MAX_NODES, node_count and node_at are ~350 occurrences across host, device and the Definition wire structs, and TaskKind::GRAPH_NODE is not a rename at all — it conflates task kind with Graph membership while also serving as the discriminator for what graph_context points at, so retiring it changes scheduler dispatch and needs its own review.
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📝 WalkthroughWalkthroughThe change renames task-ID spaces to ChangesTask ID, fanin, and Graph recording update
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🔵 Low · up to The PR fixes the recorded-node indexing issue and adds regression coverage, but one tensor-map test does not fully verify distinct chain ownership, leaving a bounded validation gap. The change is mergeable with explicit owner follow-up to strengthen that assertion. Sequence Diagram(s)sequenceDiagram
participant TaskIdEncoding
participant Orchestrator
participant TaskPayload
participant GraphDefinition
TaskIdEncoding->>Orchestrator: create GLOBAL task IDs
Orchestrator->>TaskPayload: append deduplicated fanin entries
Orchestrator->>GraphDefinition: create IN_GRAPH nodes and validate dependencies
GraphDefinition-->>Orchestrator: publish recorded tasks and roots
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✅ Passed checks (4 passed)
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In `@tests/ut/cpp/a2a3/test_hbg_tensormap.cpp`:
- Around line 111-113: Update the test around tmap.remove_entry to explicitly
select the LAST_TASK entry, assert task_entry_heads[0] and
task_entry_heads[LAST_TASK] are distinct before removal, then verify the
untouched chain still contains its producer after removal instead of relying
only on valid_count().
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📒 Files selected for processing (23)
src/a2a3/runtime/host_build_graph/host/dep_gen_host_graph.cppsrc/a2a3/runtime/host_build_graph/runtime/dep_compute.hsrc/a2a3/runtime/host_build_graph/runtime/dep_gen_host_graph.hsrc/a2a3/runtime/host_build_graph/runtime/orchestrator.hsrc/a2a3/runtime/host_build_graph/runtime/orchestrator_core/orchestrator.cppsrc/a2a3/runtime/host_build_graph/runtime/orchestrator_core/runtime_core.cppsrc/a2a3/runtime/host_build_graph/runtime/tensormap.hsrc/a5/runtime/host_build_graph/host/dep_gen_host_graph.cppsrc/a5/runtime/host_build_graph/runtime/dep_compute.hsrc/a5/runtime/host_build_graph/runtime/dep_gen_host_graph.hsrc/a5/runtime/host_build_graph/runtime/orchestrator.hsrc/a5/runtime/host_build_graph/runtime/orchestrator_core/orchestrator.cppsrc/a5/runtime/host_build_graph/runtime/orchestrator_core/runtime_core.cppsrc/a5/runtime/host_build_graph/runtime/tensormap.hsrc/common/host_build_graph/graph_execution.cppsrc/common/host_build_graph/graph_execution.hsrc/common/host_build_graph/task_id_encoding.htests/st/host_build_graph_validation/kernels/orchestration/validation_orch.cpptests/ut/cpp/CMakeLists.txttests/ut/cpp/a2a3/test_hbg_tensormap.cpptests/ut/cpp/common/test_hbg_graph_cache.cpptests/ut/cpp/common/test_hbg_graph_recording_bounds.cpptests/ut/cpp/common/test_hbg_sm_compaction.cpp
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The recording hazard-map keying fix landed identically in both arch trees, but test_hbg_graph_recording_bounds was registered only for a2a3, so nothing reached the a5 copy. Every other hbg case under tests/ut/cpp/common/ carries both an a2a3 and an a5 target; this one now does too.
host_build_graph has no ring: the host builds a whole-graph-resident task table
and the device runs it once without reclaim. Renaming TaskIdSpace::RING to
GLOBAL settled that for the identifiers, but the surrounding prose still
described tasks as living on a ring, leaving one concept spelled two ways.
Six of these comments were not stale wording but descriptions of mechanisms the
runtime does not have, so a reader who trusted them would go looking for code
that is not there:
- TaskPayload's layout comment promised that large fanins "spill into a
per-ring ring buffer slice". Fanin is always inline and hard-capped at
CHIP_MAX_FANIN, which append_fanin_or_fail's own fatal states.
- reserve_layout and wire_arena_pointers claimed to declare and wire per-ring
dep_pool regions. Polling has no dep_pool, as a comment 700 lines above
them already says.
- TaskDescriptor placed itself in a "ring buffer"; it lives in the task table.
- TaskPayload::init and the predicate write in submit_task_common attributed
uninitialized payload storage to slot reuse. hbg never reuses a slot: the
storage is raw because shared memory is not zero-filled, and that is what
the surrounding code depends on.
The rest is vocabulary. "per-ring completed_watermark" drops a modifier that
distinguishes nothing, there being one watermark. "the ring path" becomes "the
ordinary path", which is what GRAPH_EXECUTION.md and eight existing comments
already call it, one of them the line directly below a "ring path" mention. A
recorded task's id space, the SM header, the shared task table and the AICore
profiling token are each named for what they are. The ring names that describe
tensormap_and_ringbuffer, the mailbox and ready-queue ring buffers, the
doorbell verb, and the runtime_env ring_* knobs are untouched, since each is
accurate or externally consumed.
dep_compute.h also takes #pragma once: its guard macro named
tensormap_and_ringbuffer and carried the retired PTO prefix, and the a5 copy
was already converted.
Comments and docs only. The a2a3 and a5 trees remain line-for-line identical
wherever they already were. 121/121 cpput.
valid_count() counts live entries and says nothing about chain structure, so removing either of two entries takes it from 2 to 1 whether the producers hold one chain each or share one. The case was named for an invariant its assertions could not observe. It now reads task_entry_heads directly: before the removal each producer's chain head is its own entry, which is the point a shared chain would fail, since task_entry_heads[LAST_TASK] is never written when a lower index absorbs it. The removal then shows that unlinking is local to one chain.
deps_viewer and swimlane_converter document the high field of a TaskId, and both still spelled hbg's two id spaces RING and GRAPH_NODE. The numeric encoding is unchanged and neither tool's parsing moved, so nothing misbehaves -- but the docstrings now disagree with task_id_encoding.h, and a reader who trusts them concludes either that hbg still has a ring or that space 1 is TaskKind::GRAPH_NODE, which is a different field with a different meaning. _decode_graph_node_task_id's packing formula named outer_local and node_index; the constructor it describes takes graph_local_id and task_index. Its own name and the Graph-node vocabulary around it are left alone, per the id-space rename that kept GraphNodeDefinition, graph_node_index and TaskKind::GRAPH_NODE.
zhusy54
approved these changes
Aug 27, 2026
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Four changes to
host_build_graph, each independent enough to review on its own.1. Drop the
FaninBuilderstructFaninBuilderhad shrunk to four fields and one method. Two of those fields,countand
slots, were copies ofpayload.fanin_countandpayload.fanin_data(), andSTEP 6 copied the count back to the payload at the end of every submit.
append_fanin_or_failnow takes the consumer payload's fanin region and its countdirectly, so the count accumulates in place and the copy-back is gone.
mark_seenbecomes the free function
fanin_mark_seen, andnext_fanin_seen_epochdrops itsreturn value now that the epoch it advances to is read from
orch.fanin_seen_current_epoch. The region is still resolved once per task, not perproducer: it is named by a
SelfRelativePtrdelta.2. Fix a heap out-of-bounds write in the Graph recording hazard map
The recording's hazard map holds
GRAPH_MAX_NODEStask chains and indexes them by aproducer's low id field directly, but a recorded node was minted in the RING space as
start_local_task_id + node_index. Any Graph that begins after the run's firstGRAPH_MAX_NODEStasks — the ordinary shape for a decode workload — registered itsnodes past the last chain and wrote outside
task_entry_heads.Confirmed under ASAN, full stack:
A recorded node now takes a
GRAPH_NODEid whose low field is the node index alone,so the key is in range however far into a run the Graph begins. The recording baseline
that existed only to tell a node from a pre-Graph task by numeric range is gone: the
two now differ by id space, decided at the mint rather than derived by subtraction.
Two consequences beyond the out-of-bounds write:
inside a node's index range and be wired as an internal fanin. That
misclassification was unreachable in practice, but only because of what a body can
hold — not by construction.
trips
append_fanin_or_fail's id-space guard instead of resolving to an unrelatedtask slot and wiring a wrong edge.
An over-cap body skips hazard-map registration: its node index has run past the field
make_graph_nodepacks it into, and the Definition is abandoned already.link_entryandremove_from_taskcarry adebug_asserton the chain index, so afuture caller inserting under the wrong id space is caught where it happens rather
than corrupting the heap.
test_hbg_tensormap's slot-aliasing case rested on a mask hbg does not have — its owninserts ran one chain past the fixture's dimension. It now pins the invariant that
holds: a local id is its own chain index, so distinct producers never share a chain.
The new
test_hbg_graph_recording_boundsruns against both arch trees, matching everyother hbg case under
tests/ut/cpp/common/— the fix is mirrored in a5, so its testhas to be too.
3. Name the task id spaces by Graph membership
TaskIdSpace::RINGdated from a ring designhost_build_graphno longer has — theheader's own comment had to apologize for the name. And there is no separate "node"
concept to name: everything the runtime schedules is a task, and the only question the
high bits answer is whether a task belongs to a Graph task or stands on its own.
TaskIdSpacekeeps its name: the field holds which id namespace an id belongs to,which is what "space" says, and "type" would collide conceptually with
TaskKind.is_global_taskgains a comment naming what its callers actually depend on — that theid resolves to a shared-memory task table slot — since the old name carried that by
implication and the new one does not.
The deeper
nodevocabulary is untouched:GraphNodeStorage,GraphNodeDefinition,graph_node_index,GRAPH_MAX_NODES,node_countandnode_atare ~350 occurrencesacross host, device and the Definition wire structs.
TaskKind::GRAPH_NODEis not arename at all — it conflates task kind with Graph membership while also serving as the
discriminator for what
graph_contextpoints at, so retiring it changes schedulerdispatch and needs its own review.
4. Retire the ring vocabulary from comments and docs
host_build_graphhas no ring, which is why #3 renamesTaskIdSpace::RING. Thatsettled the identifiers, but the surrounding prose still described tasks as living on
a ring — so the concept stayed spelled two ways.
Six of those comments described mechanisms the runtime does not have, which is the
part worth reviewing: a reader who trusted them would go looking for absent code.
TaskPayload's layout comment promised large fanins "spill into a per-ring ringbuffer slice". Fanin is always inline and hard-capped at
CHIP_MAX_FANIN—append_fanin_or_fail's own fatal says exactly that.reserve_layoutandwire_arena_pointersclaimed to declare and wire per-ringdep_poolregions. Polling has nodep_pool, as a comment 700 lines above themalready states.
TaskDescriptorplaced itself in a "ring buffer"; it lives in the task table.TaskPayload::initand the predicate write insubmit_task_commonattributeduninitialized payload storage to slot reuse. hbg never reuses a slot: the storage is
raw because shared memory is not zero-filled, and that is what the surrounding
code depends on.
The rest is vocabulary.
per-ring completed_watermarkdrops a modifier thatdistinguishes nothing, there being one watermark.
the ring pathbecomesthe ordinary path, which is whatGRAPH_EXECUTION.mdand eight existing comments already call it —one of them the line directly below a
ring pathmention.Untouched, because each is accurate or externally consumed: the ring names describing
tensormap_and_ringbuffer, the mailbox and ready-queue ring buffers, the doorbell verb(
ring_one_doorbell,maybe_rendezvous_ring, ...), theruntime_env.ring_*knobs, andthe
TASK ring=%dstall-log field.dep_compute.halso takes#pragma once: its guard macro namedtensormap_and_ringbufferand carried the retiredPTOprefix, and the a5 copy wasalready converted.
Comments and docs only. The a2a3 and a5 trees stay line-for-line identical wherever
they already were.
Testing
ctestontests/ut/cpp: 121/121 (120 + the new a5 target).tests/ut/cpp: the twolink_entryoverflows reported before thefix (one from the new recording test, one the pre-existing
test_hbg_tensormapaliasing case triggered on itself) are both gone. This is the only thing that proves
the write is actually gone, and CI does not cover it —
sanitizers.ymlruns simscene tests, not cpput.
a2a3simanda5simwith--manual include.pre-commitover every changed file, includingcheck-retired-names,clang-tidy,cpplintandmarkdownlint.host_build_graph_validationincludinggraph_node_dependency, which is thestanding regression barrier for "a Graph-internal id used as an explicit dependency
is a fatal".