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Add missing write barrier in set_i_initialize_copy #13558

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Merged
merged 1 commit into from
Jun 9, 2025
Merged

Add missing write barrier in set_i_initialize_copy #13558

merged 1 commit into from
Jun 9, 2025

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jhawthorn
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This fixes a missing write barrier in the new Set implementation I detected with my new "wbcheck" tool (see #13557)

$ RUBY_GC_LIBRARY=wbcheck ./miniruby -e 'Set["a","b","c"].collect!(&:upcase)'
WBCHECK ERROR: Missed write barrier detected!
  Parent object: 0x50700001cdb0 (wb_protected: true)
    rb_obj_info_dump: (Set)set
  Reference counts - stored: 4, current: 4, missed: 3
  Missing reference to: 0x50400007f2d0
    rb_obj_info_dump: (String) len: 1, capa: 15 "A"
  Missing reference to: 0x50400007f350
    rb_obj_info_dump: (String) len: 1, capa: 15 "B"
  Missing reference to: 0x50400005f990
    rb_obj_info_dump: (String) len: 1, capa: 15 "C"

WBCHECK SUMMARY: Found 1 objects with missed write barriers (3 total violations)

It was a bit harder to reproduce with the standard GC, but I wanted to confirm this is a real issue and not a false-positive:

old_set = Set.new
3.times { GC.start }
old_set.replace(100.times.map { Object.new }.to_set)
GC.start(full_mark: false)
old_set.to_a.inspect
ruby --disable-gems test_set_wb.rb
test_set_wb.rb:5: [BUG] Segmentation fault at 0x0000000000000000
ruby 3.5.0dev (2025-05-26T20:44:05Z ractor_port 52248b13ff) +PRISM [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0004 p:---- s:0014 e:000013 CFUNC  :inspect
c:0003 p:---- s:0011 e:000010 CFUNC  :inspect
c:0002 p:0050 s:0007 E:001878 EVAL   test_set_wb.rb:5 [FINISH]
c:0001 p:0000 s:0003 E:001760 DUMMY  [FINISH]

-- Ruby level backtrace information ----------------------------------------
test_set_wb.rb:5:in '<main>'
test_set_wb.rb:5:in 'inspect'
test_set_wb.rb:5:in 'inspect'

@jhawthorn
Add missing write barrier in set_i_initialize_copy
cb2703a 
When we copy the table from one set to another we need to run write
barriers.
@jhawthorn jhawthorn mentioned this pull request Jun 8, 2025
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@jhawthorn jhawthorn merged commit c962735 into ruby:master Jun 9, 2025
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@tenderlove tenderlove tenderlove approved these changes

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@jhawthorn @tenderlove