add VM Lock around rb_const_remove operations (Module#remove_const)
#13717
+99
−73
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Without a VM Lock, there's an unlocked `rb_id_table_delete` for the
class's const_tbl which can cause problems. Example:
```ruby
class C
CONSTANT = 3
end
$VERBOSE = nil
rs = []
100.times do
rs << Ractor.new do
10_000.times do
if defined?(C::CONSTANT)
C.send(:remove_const, :CONSTANT) rescue NameError
else
C.send(:const_set, :CONSTANT, 3)
end
end
end
end
while rs.any?
r, obj = Ractor.select(*rs)
rs.delete(r)
end
```
Without lock:
../ruby-release/test.rb:14: [BUG] Segmentation fault at 0x0000000000000001
-- Control frame information -----------------------------------------------
miniruby(82790,0x16f49f000) malloc: *** error for object 0x600000f880a0: pointer being freed was not allocated
miniruby(82790,0x16f49f000) malloc: *** set a breakpoint in malloc_error_break to debug
|
Seems like we might be missing locking for const lookup as well. class C
CONSTANT = 3
end
$VERBOSE = nil
rs = []
100.times do
rs << Ractor.new do
10_000.times do
if defined?(C::CONSTANT)
C.send(:remove_const, :CONSTANT) rescue NameError
else
C.send(:const_set, :CONSTANT, 3)
end
C.const_get(:CONSTANT) rescue NameError
C.const_get(:CONSTANT) rescue NameError
end
end
end
while rs.any?
r, obj = Ractor.select(*rs)
rs.delete(r)
end |
|
Should |
|
Yeah it's a good point, but for whatever reason this has always been allowed in ractors, and it was by design not by accident. As for why, I don't know but maybe it's to do with supporting autoloading in ractors. If you support autoloading constants, it's a small step away from supporting setting constants directly. |
jhawthorn
reviewed
Jul 3, 2025
| @@ -44,7 +44,7 @@ void rb_free_const_table(struct rb_id_table *tbl); | |||
| VALUE rb_const_source_location(VALUE, ID); | |||
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|||
| int rb_autoloading_value(VALUE mod, ID id, VALUE *value, rb_const_flag_t *flag); | |||
| rb_const_entry_t *rb_const_lookup(VALUE klass, ID id); | |||
| rb_const_entry_t *rb_const_lookup(VALUE klass, ID id, rb_const_entry_t *entry_out); | |||
There was a problem hiding this comment.
Should we make this return an int bool like st_lookup?
|
|
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Without a VM Lock, there's an unlocked
rb_id_table_deletefor the class's const_tbl which can cause problems. Example:Without lock:
../ruby-release/test.rb:14: [BUG] Segmentation fault at 0x0000000000000001 -- Control frame information ----------------------------------------------- miniruby(82790,0x16f49f000) malloc: *** error for object 0x600000f880a0: pointer being freed was not allocated miniruby(82790,0x16f49f000) malloc: *** set a breakpoint in malloc_error_break to debug