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Avoid racy double-load of binding restriction in import_module #56395

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Oct 31, 2024
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Avoid racy double-load of binding restriction in import_module #56395

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9 changes: 7 additions & 2 deletions src/toplevel.c
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Original file line number Diff line number Diff line change
Expand Up @@ -665,11 +665,16 @@ static void import_module(jl_module_t *JL_NONNULL m, jl_module_t *import, jl_sym
jl_sym_t *name = asname ? asname : import->name;
// TODO: this is a bit race-y with what error message we might print
jl_binding_t *b = jl_get_module_binding(m, name, 1);
if (jl_get_binding_value_if_const(b) == (jl_value_t*)import)
return;
jl_binding_partition_t *bpart = jl_get_binding_partition(b, jl_current_task->world_age);
jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
if (decode_restriction_kind(pku) != BINDING_KIND_GUARD && decode_restriction_kind(pku) != BINDING_KIND_FAILED) {
// Unlike regular constant declaration, we allow this as long as we eventually end up at a constant.
pku = jl_walk_binding_inplace(&b, &bpart, jl_current_task->world_age);
if (decode_restriction_kind(pku) == BINDING_KIND_CONST || decode_restriction_kind(pku) == BINDING_KIND_CONST_IMPORT) {
// Already declared (e.g. on another thread) or imported.
if (decode_restriction_value(pku) == (jl_value_t*)import)
return;
}
jl_errorf("importing %s into %s conflicts with an existing global",
jl_symbol_name(name), jl_symbol_name(m->name));
}
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