TASK-189246 lock gc before traversing openupval#6
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| luaC_blockcollector(L); | ||
| unlinkupval(uv); /* remove from open list */ | ||
| luaC_unblockcollector(L); | ||
| } |
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GC thread can deadlock blocking collector
High Severity
luaF_freeupval now calls luaC_blockcollector when freeing an open UpVal. This function is invoked from the GC reclamation path (reclaim_object for LUA_TUPVAL), so the collector thread can end up blocking on itself while a global trace is active (eg. intend_to_stop set / trace_rwlock held), causing a hard deadlock.
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Note
Medium Risk
Touches core GC/stop-the-world synchronization and upvalue lifecycle; small diff but incorrect blocking/unblocking or recursion balancing could introduce deadlocks or GC stalls under load.
Overview
Prevents a concurrency race between global GC tracing and mutation of a thread’s open-upvalue list by wrapping
luaF_closeand open-pathluaF_freeupvalunlinking withluaC_blockcollector/luaC_unblockcollector.Adds per-thread recursion accounting to the global-trace mutator stop/start path (
try_block_mutators/unblock_mutators) so nested collector-blocking operations remain balanced.Written by Cursor Bugbot for commit a118619. This will update automatically on new commits. Configure here.