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refactor(allocator): improve safety of dealloc_chunk_list#21779

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Apr 26, 2026
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refactor(allocator): improve safety of dealloc_chunk_list#21779
graphite-app[bot] merged 1 commit into
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om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_

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@overlookmotel overlookmotel commented Apr 26, 2026 •
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Improve the safety of Arena's dealloc_chunk_list function:

  • Ensure &ChunkFooter reference is not live when the chunk containing that ChunkFooter is deallocated.
  • Scope unsafe { ... } blocks to cover just the statements that require them.
  • Document the safety invariants.

I don't believe there was a soundness issue here (as &ChunkFooter references were short-lived), but this change makes the importance of avoiding live references clear, and explicitly guards against it.

This was referenced Apr 26, 2026
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overlookmotel commented Apr 26, 2026 •
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This was referenced Apr 26, 2026
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@overlookmotel overlookmotel self-assigned this Apr 26, 2026
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Merging this PR will not alter performance

✅ 48 untouched benchmarks
⏩ 3 skipped benchmarks1

Comparing om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ (5e7dbac) with om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators (6889c46)

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Footnotes

  1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

@overlookmotel
overlookmotel force-pushed the om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators branch from 67ff1f2 to a82c143 Compare April 26, 2026 12:27
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overlookmotel force-pushed the om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ branch from 8f6d4d9 to a44ec68 Compare April 26, 2026 12:27
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overlookmotel marked this pull request as ready for review April 26, 2026 18:46
Copilot AI review requested due to automatic review settings April 26, 2026 18:46
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Pull request overview

This PR refactors Arena’s chunk deallocation helper to make aliasing/lifetime boundaries around ChunkFooter references explicit, reduce the scope of unsafe blocks, and document the safety assumptions involved in freeing arena chunks.

Changes:

  • Refactors dealloc_chunk_list to ensure &ChunkFooter borrows are not live across dealloc.
  • Narrows unsafe blocks to only the operations that require them.
  • Adds safety documentation/comments explaining required invariants.

Comment thread crates/oxc_allocator/src/arena/drop.rs
Comment thread crates/oxc_allocator/src/arena/drop.rs Outdated
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overlookmotel changed the base branch from om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators to graphite-base/21779 April 26, 2026 20:47
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overlookmotel force-pushed the om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ branch from a44ec68 to e689974 Compare April 26, 2026 20:48
@overlookmotel
overlookmotel changed the base branch from graphite-base/21779 to om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators April 26, 2026 20:48
This was referenced Apr 26, 2026
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overlookmotel force-pushed the om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ branch from e689974 to 75bb873 Compare April 26, 2026 21:15
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@overlookmotel
refactor(allocator): improve safety of dealloc_chunk_list (#21779)
5e7dbac 
Improve the safety of `Arena`'s `dealloc_chunk_list` function:

- Ensure `&ChunkFooter` reference is not live when the chunk containing that `ChunkFooter` is deallocated.
- Scope `unsafe { ... }` blocks to cover just the statements that require them.
- Document the safety invariants.

I don't believe there was a soundness issue here (as `&ChunkFooter` references were short-lived), but this change makes the importance of avoiding live references clear, and explicitly guards against it.
@graphite-app
graphite-app Bot force-pushed the om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators branch from 1d77796 to 6889c46 Compare April 26, 2026 21:52
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graphite-app Bot requested a review from camc314 as a code owner April 26, 2026 21:52
@graphite-app
graphite-app Bot force-pushed the om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ branch from 75bb873 to 5e7dbac Compare April 26, 2026 21:53
Base automatically changed from om/04-26-refactor_allocator_reduce_scope_of_unsafe_blocks_in_arena_chunk_iterators to main April 26, 2026 22:09
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graphite-app Bot merged commit 5e7dbac into main Apr 26, 2026
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graphite-app Bot deleted the om/04-26-refactor_allocator_improve_safety_of_dealloc_chunk_list_ branch April 26, 2026 22:10
@overlookmotel overlookmotel added C-cleanup Category - technical debt or refactoring. Solution not expected to change behavior A-allocator Area - Allocator labels Apr 27, 2026
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