Fix write barriers in rb_hash_add_new_element #13659
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The write barriers must be run after the st_update callback returns,
as the objects are not on the object until then and there may be
allocation when there is a new object inserted.
This is hard to reproduce, and I haven't seen an actual crash due to it,
but it is detected by wbcheck
RUBY_GC_LIBRARY=wbcheck WBCHECK_VERIFY_AFTER_WB=1 ./miniruby -e '("a".."zz").uniq.to_a'
WBCHECK ERROR: Missed write barrier detected!
Parent object: 0x720db01f99c0 (wb_protected: true)
rb_obj_info_dump: 0x0000720db01f99c0 T_HASH/[S] 18
Reference counts - snapshot: 32, writebarrier: 2, current: 36, missed: 2
Missing reference to: 0x716db02e3450
rb_obj_info_dump: 0x0000716db02e3450 T_STRING/String len: 1, capa: 15 "q"
Missing reference to: 0x716db02e3450
rb_obj_info_dump: 0x0000716db02e3450 T_STRING/String len: 1, capa: 15 "q"
A part of why this is hard to reproduce and it's unlikely to crash is
that the insertion only rarely allocates.
Co-authored-by: Luke Gruber <[email protected]>
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The write barriers must be run after the st_update callback returns, as the objects are not on the object until then and there may be allocation when there is a new object inserted.
This is hard to reproduce, and I haven't seen an actual crash due to it, but it is detected by wbcheck
A part of why this is hard to reproduce and it's unlikely to crash is that the insertion only rarely allocates.