Bug #19894: Memory leak in complemented method entries

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.0: UNKNOWN, 3.1: DONE, 3.2: DONE

[peterzhu2118 (Peter Zhu)]

GitHub pull request: https://github.com/ruby/ruby/pull/8481

When a copy of a complemented method entry is created, there are two issues:

1. IMEMO_FL_USER3 is not copied, so the complemented status is not copied over.
2. In rb_method_entry_clone we increment both alias_count and complemented_count. However, when we free the method entry in rb_method_definition_release, we only decrement one of the two counters, resulting in the rb_method_definition_t being leaked.

The following script reproduces this issue:

10.times do
  20_000.times do
    $c = Class.new do
      def foo; end
    end

    $m = Module.new do
      refine $c do
        def foo; end
      end
    end

    Class.new do
      using $m

      def initialize
        o = $c.new
        o.method(:foo).unbind
      end
    end.new
  end

  puts `ps -o rss= -p #{$$}`
end

Before this fix:

 17328
 19248
 21408
 23296
 25600
 27408
 29424
 31520
 33728
 35664

After this fix:

 16240
 17680
 18800
 19744
 20640
 21840
 22896
 24336
 25280
 26096

[peterzhu2118 (Peter Zhu)]

• Backport changed from 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: REQUIRED to 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: REQUIRED

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|96c5a4be7b0d72502001734770af0f4a735c544c.

---

Fix memory leak in complemented method entries

[Bug #19894]

When a copy of a complemented method entry is created, there are two
issues:

1. IMEMO_FL_USER3 is not copied, so the complemented status is not
   copied over.
2. In rb_method_entry_clone we increment both alias_count and
   complemented_count. However, when we free the method entry in
   rb_method_definition_release, we only decrement one of the two
   counters, resulting in the rb_method_definition_t being leaked.

Co-authored-by: Adam Hess [e-mail]

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: REQUIRED to 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: DONE

ruby_3_2 9ee58b2054c1bbe722ae5a2a4ec6a750ee583220 merged revision(s) 96c5a4be7b0d72502001734770af0f4a735c544c.

[usa (Usaku NAKAMURA)]

• Backport changed from 3.0: UNKNOWN, 3.1: REQUIRED, 3.2: DONE to 3.0: UNKNOWN, 3.1: DONE, 3.2: DONE

ruby_3_1 a3e1444663005d3440b56c3a8e1b88bb28935912 merged revision(s) 96c5a4be7b0d72502001734770af0f4a735c544c.