[ruby-core:113055] [Ruby master Bug#19554] Invalid memory access detected by Valgrind when using Fibers

Issue #19554 has been updated by peterzhu2118 (Peter Zhu).


> It's unlikely that Valgrind will work with CRuby out of the box without Valgrind specific code e.g. for marking stacks, poisoning "freed" memory, etc.

Valgrind (without the memory leak detection feature, so only detecting invalid memory access) actually works very well with CRuby (excluding Fibers), which is why I opened this ticket.

For most C extensions, they are able to use Valgrind with memory leak detection using [ruby_memcheck](https://github.com/Shopify/ruby_memcheck), which applies heuristics to remove false-positive memory leaks in Ruby.

In fact, issues like #18264 and #18936 were found by Valgrind.



----------------------------------------
Bug #19554: Invalid memory access detected by Valgrind when using Fibers
https://bugs.ruby-lang.org/issues/19554#change-102593

* Author: peterzhu2118 (Peter Zhu)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
This issue was originally reported here: https://github.com/Shopify/ruby_memcheck/issues/14

Running the script shown below using `valgrind --trace-children=yes --num-callers=500 ruby test.rb` outputs a lot of invalid memory access errors. I've shown a few sample errors below.

I am able to reproduce this issue on the master branch (commit [1e9a218ade](https://github.com/ruby/ruby/commit/1e9a218ade3af90c18f42e3fea08e2fcea81222a)), 3.2, 3.1, 3.0.


```ruby
require "bundler/inline"
gemfile do
  source "https://rubygems.org"
  gem "graphql"
end

module Example
  class FooType < GraphQL::Schema::Object
    field :id, ID, null: false
  end

  class FooSource < GraphQL::Dataloader::Source
    def fetch(ids)
      ids
    end
  end

  class QueryType < GraphQL::Schema::Object
    field :foo, Example::FooType do
      argument :foo_id, GraphQL::Types::ID, required: false, loads: Example::FooType
    end

    def foo(foo: nil); end
  end

  class Schema < GraphQL::Schema
    query Example::QueryType
    use GraphQL::Dataloader

    def self.object_from_id(id, ctx)
      ctx.dataloader.with(Example::FooSource).request(id)
    end
  end
end

Example::Schema.execute(<<-GRAPHQL)
{
  foo(fooId: "Other") {
    id
  }
}
GRAPHQL
```

```
==203957== Use of uninitialised value of size 8
==203957==    at 0x3453FD: vm_exec_core (vm.inc:4411)
==203957==    by 0x357EFB: rb_vm_exec (vm.c:2366)
==203957==    by 0x354E44: invoke_block (vm.c:1384)
==203957==    by 0x355759: invoke_iseq_block_from_c (vm.c:1440)
==203957==    by 0x355759: invoke_block_from_c_proc (vm.c:1538)
==203957==    by 0x355759: vm_invoke_proc (vm.c:1568)
==203957==    by 0x355DF4: rb_vm_invoke_proc (vm.c:1589)
==203957==    by 0x48F695: rb_fiber_start (cont.c:2513)
==203957==    by 0x48CCF8: fiber_entry (cont.c:831)
==203957==
==203957== Invalid write of size 8
==203957==    at 0x48C407: fiber_pool_stack_reset (cont.c:325)
==203957==    by 0x48C4E9: fiber_pool_vacancy_reset (cont.c:364)
==203957==    by 0x48CBB0: fiber_pool_stack_release (cont.c:752)
==203957==    by 0x48CECF: fiber_stack_release (cont.c:874)
==203957==    by 0x48FC9F: fiber_switch (cont.c:2726)
==203957==    by 0x4901F9: fiber_resume_kw (cont.c:2906)
==203957==    by 0x490235: rb_fiber_resume_kw (cont.c:2912)
==203957==    by 0x4903B7: rb_fiber_m_resume (cont.c:2973)
==203957==    by 0x3337D6: ractor_safe_call_cfunc_m1 (vm_insnhelper.c:3166)
==203957==    by 0x33440A: vm_call_cfunc_with_frame_ (vm_insnhelper.c:3357)
==203957==    by 0x3345E1: vm_call_cfunc_with_frame (vm_insnhelper.c:3385)
==203957==    by 0x3398E5: vm_sendish (vm_insnhelper.c:5225)
==203957==    by 0x341203: vm_exec_core (insns.def:835)
==203957==    by 0x357EFB: rb_vm_exec (vm.c:2366)
==203957==    by 0x354E44: invoke_block (vm.c:1384)
==203957==    by 0x355759: invoke_iseq_block_from_c (vm.c:1440)
==203957==    by 0x355759: invoke_block_from_c_proc (vm.c:1538)
==203957==    by 0x355759: vm_invoke_proc (vm.c:1568)
==203957==    by 0x355DF4: rb_vm_invoke_proc (vm.c:1589)
==203957==    by 0x48F695: rb_fiber_start (cont.c:2513)
==203957==    by 0x48CCF8: fiber_entry (cont.c:831)
==203957==  Address 0x9bad008 is in a rw- anonymous segment
```




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