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Heap corruption (munmap_chunk: invalid pointer) at startup in Prefill::init — crashes with 1/2/4 GPUs

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#828 1 comment 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
cpp
Domain
backend

Research direction

Start in src/prefill/prefill.cpp at Prefill::init() and trace how the borrowed buffer from ExpertCache::device_slot() is used and how the #583 byte-budget ring changes affect that path. The report says STRATA_RING_BYTES=0 still crashes, so compare startup behavior with and without that setting. Done when startup completes without heap corruption across the reported GPU configurations.

Written by the indexing model from the issue text.

Description

Crash

Engine crashes at startup with munmap_chunk(): invalid pointer (heap corruption) during prompt path initialization. Happens consistently, 100% reproducible.

Log (last lines before crash)

strata generate: layer split: CUDA0 runs layers 0-11
strata generate: R4 hit path ON - resident experts are computed on the GPU
strata generate: 8 expert-pool workers + the host thread
strata generate: session is up (engine 0.1.39)
strata generate: token graph hit path: 16530 resident experts, decided on the device
strata serve: the prompt path allocates its own buffers (too few cache slots to borrow)
munmap_chunk(): invalid pointer

With default settings (no STRATA_SPLIT_OWN), it crashes at:

strata serve:   CUDA3 prompt path borrows 2914 of its 4526 slots (4.03 GiB)
munmap_chunk(): invalid pointer

System

  • 4x RTX 3060 12GB (sm_86)
  • 128GB DDR4-3200
  • Debian 13 (trixie), glibc 2.41
  • CUDA 13.0 toolkit, NVIDIA driver 595.91.07
  • Engine 0.1.39 (commit 6f32ec0, latest main as of 2026-10-04)
  • Model: Qwen3.8-Flash-Next-GSQ-RCO-IQ2_XS, 262144 context, --vision yes
  • Running in LXC container

What I've tried

  • 1, 2, and 4 GPUs (--gpus 0 / 0,1 / all) — all crash identically
  • With and without STRATA_SPLIT_OWN=1 — both crash
  • STRATA_RING_BYTES=0 (opt out of #583) — still crashes
  • 32k vs 262k context — both crash
  • Increased --vram-reserve-mib to 2000 — still crashes
  • MALLOC_CHECK_=3 confirms heap corruption (process aborts instead of munmap error)

Analysis

The crash is inside Prefill::init() (src/prefill/prefill.cpp). The borrow buffer (from ExpertCache::device_slot()) is valid — I verified the slot index is in-bounds and the pointer is non-null. The corruption happens after Prefill::init receives the borrow buffer.

The #583 "byte-budget ring" changes are the likely culprit (all recent changes to prefill.cpp are from #583), but STRATA_RING_BYTES=0 does not fully disable the code path.

This is different from Issue #70 (which crashes mid-decode after successfully serving). This crashes at startup, before serving any requests.

Dominant language
C++
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Forks
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Avg merge
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Merged PRs (30d)
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