Concurrent graph-root loads in the JS eval kernel segfaulted Bun
(SIGSEGV at 0xFFFFFFFFFFFFFFF8, getImportedModule on a null record in
JSC::AbstractModuleRecord::innerModuleLinking). Two roots loaded at once
over an overlapping local-import graph — e.g.
Promise.all([import("./a.ts"), import("./b.ts")]) sharing a dependency —
each launched its own module.link() over the same shared
vm.SourceTextModule instances. The async link resolver yields
mid-instantiation, letting the two link passes interleave and re-enter
Bun's node:vm linker, which crashes instead of throwing.
The earlier single-pass fix (15.7.2) only serialized linking within one
graph root; it did not guard two concurrent roots over shared modules.
LocalModuleLoader now routes every module.link() through a promise-chain
mutex (#serializeLink), so the linker is never re-entered
mid-instantiation. The lock is held only across link(), not evaluate(),
so a dynamic import during evaluation re-acquires it without deadlock,
and the chain swallows rejections so a failed link cannot wedge later
imports. Reproduced and verified against the user crash trace: the
concurrent-diamond repro went from 5/6 crashes to 0/N with correct
namespaces.
can1357
2900730aa6