[ruby-core:89924] [Ruby trunk Bug#15325] Ruby 2.5.3 seg fault after find block returns

[stanhu@gmail.com]

Issue #15325 has been updated by stanhu (Stan Hu).


Something is quite odd. I tried a number of variations:

1. `break build` appears to work with Ruby 2.4.5 and 2.5.3.
1. Instead of `break build`, use `true`: In Ruby 2.5.3, this by itself seems to cause selection to be nil. I got a segfault with Ruby 2.4.5 here in the garbage collector (`rb_gc_mark_node`).
1. Instead of `break build`, use `break true`: selection is `nil` in both Ruby 2.4.5 and 2.5.3.
1. Removing the begin/rescue clause entirely and testing this. The below did not work either:

~~~
selection = builds.find do |build|
   if assign_runner!(build, params)
     register_success(build)

     true
   else
     false
   end
 end
~~~



----------------------------------------
Bug #15325: Ruby 2.5.3 seg fault after find block returns
https://bugs.ruby-lang.org/issues/15325#change-75008

* Author: stanhu (Stan Hu)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-darwin15]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
In https://gitlab.com/gitlab-org/gitlab-ce/blob/233af8f1731734aaad7e5055af39f26c16608649/app/services/ci/register_job_service.rb#L48, we see a repeatable seg fault on both MacOS and Ubuntu with Rails 5.0.7 in a development environment. The seg fault appears to occur after the `find` returns:

~~~
builds.find do |build|
        next unless runner.can_pick?(build)

        begin
          # In case when 2 runners try to assign the same build, second runner will be declined
          # with StateMachines::InvalidTransition or StaleObjectError when doing run! or save method.
          if assign_runner!(build, params)
            register_success(build)

            return Result.new(build, true) # <--- SEG FAULT HAPPENS AFTER HERE
          end
        rescue StateMachines::InvalidTransition, ActiveRecord::StaleObjectError
~~~

The segfault shows some bad memory access:

~~~
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib              0x00007fff5d0e8b86 __pthread_kill + 10
1   libsystem_pthread.dylib             0x00007fff5d19ec50 pthread_kill + 285
2   libsystem_c.dylib                   0x00007fff5d0521c9 abort + 127
3   ruby                                0x000000010f5ec6a9 die + 9
4   ruby                                0x000000010f5ec908 rb_bug_context + 600
5   ruby                                0x000000010f6db7a1 sigsegv + 81
6   libsystem_platform.dylib            0x00007fff5d193b3d _sigtramp + 29
7   ???                                 000000000000000000 0 + 0
8   ruby                                0x000000010f75461e vm_exec + 142
9   ruby                                0x000000010f761f25 invoke_block_from_c_bh + 405
10  ruby                                0x000000010f74f719 rb_yield + 153
11  ruby                                0x000000010f5e33b9 find_i + 41
12  ruby                                0x000000010f7620ca invoke_block_from_c_bh + 826
13  ruby                                0x000000010f74f719 rb_yield + 153
14  ruby                                0x000000010f57cce9 rb_ary_each + 41
15  ruby                                0x000000010f759f51 vm_call_cfunc + 305
16  ruby                                0x000000010f742a0d vm_exec_core + 9149
17  ruby                                0x000000010f75461e vm_exec + 142
18  ruby                                0x000000010f761d41 rb_call0 + 161
19  ruby                                0x000000010f74fe54 iterate_method + 52
20  ruby                                0x000000010f74fd9b rb_iterate0 + 347
21  ruby                                0x000000010f74fe1a rb_block_call + 74
22  ruby                                0x000000010f5e0518 enum_find + 104
23  ruby                                0x000000010f759f51 vm_call_cfunc + 305
24  ruby                                0x000000010f7436bd vm_exec_core + 12397
~~~

We do NOT see the problem after downgrading to 2.4.5.


---Files--------------------------------
ruby_2018-11-20-132027_jet.crash (66.1 KB)
ruby-2.5.3-segfault.txt (774 KB)


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