Fix release fence ordering in inner_enqueue() to prevent size_approx() race on AArch64 - #172
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cppmage wants to merge 1 commit into
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Fix release fence ordering in inner_enqueue() to prevent size_approx() race on AArch64#172cppmage wants to merge 1 commit into
cppmage wants to merge 1 commit into
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Move fence(memory_order_release) before both writes that publish a newly allocated block (tailBlock_->next and tailBlock), not just the second one. size_approx() reaches blocks via the next-chain and never reads tailBlock, so it wasn't covered by the existing fence placement. Fixes cameron314#171
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Fixes #171
What changed
Move
fence(memory_order_release)ininner_enqueue()'sCanAllocbranch so it precedes both writes that publish a newly allocated block
(
tailBlock_->next = newBlockandtailBlock = newBlock), instead ofonly the second one. See #171 for the full root-cause
analysis and repro.
Also expanded the comment at that call site to note that
size_approx()(and any otherBlock::next-chain traversal) dependson this ordering too, not just
try_dequeue().Testing
size_approxstress test run in a loop (1000 iterations).same loop (1000 iterations).
size_approxstress test has other pre-existingassertion failures, unrelated to this change and not addressed here.