Segmentation fault with ruby-2.6.3

[cesarizu]

When updating an app to run with ruby 2.6.3 (from 2.4.4) I get the following error:

/home/user/.rvm/gems/ruby-2.6.3@project/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var.rb:87: [BUG] Segmentation fault at 0x000000002222002d
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0002 p:0006 s:0007 e:000005 BLOCK  /home/user/.rvm/gems/ruby-2.6.3@project/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var. [FINISH]
c:0001 p:---- s:0003 e:000002 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
/home/user/.rvm/gems/ruby-2.6.3@project/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var.rb:87:in `block (2 levels) in threadlocal_finalizer'

-- Machine register context ------------------------------------------------
 RIP: 0x00007fde9b71bf49 RBP: 0x0000000000021deb RSP: 0x00007fde97cb77e8
 RAX: 0x000000000b275620 RBX: 0x0000000001719630 RCX: 0x000000002222002d
 RDX: 0x0000000000000000 RDI: 0x000000000b275620 RSI: 0x000000000a667f70
  R8: 0x0000000001718d50  R9: 0x0000000001719618 R10: 0x0000000000000008
 R11: 0x000000000a568038 R12: 0x000000000b2750f0 R13: 0x000000000a567ff8
 R14: 0x0000000001719640 R15: 0x000000000a667f70 EFL: 0x0000000000010206

-- C level backtrace information -------------------------------------------

I tried using Concurrent.use_stdlib_logger(Logger::DEBUG) to get more information but nothing else is printed to the console. How can I start debugging this problem?

* Operating system:                linux
* Ruby implementation:             Ruby 2.6.3
* `concurrent-ruby` version:       1.1.5
* `concurrent-ruby-ext` installed: no
* `concurrent-ruby-edge` used:     no

[mwsteb]

Not sure if this should be a separate issue or not, but I'm here to report that it happens on Ruby 2.5.5p157 as well. Here's the trace:

/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:322: [BUG] Segmentation fault at 0x000000010992aa3a
ruby 2.5.5p157 (2019-03-15 revision 67260) [x86_64-darwin18]

-- Crash Report log information --------------------------------------------
   See Crash Report log file under the one of following:
     * ~/Library/Logs/DiagnosticReports
     * /Library/Logs/DiagnosticReports
   for more details.
Don't forget to include the above Crash Report log file in bug reports.

-- Control frame information -----------------------------------------------
c:0007 p:---- s:0032 e:000031 CFUNC  :pop
c:0006 p:0007 s:0028 e:000027 BLOCK  /Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor [FINISH]
c:0005 p:---- s:0022 e:000021 CFUNC  :loop
c:0004 p:0006 s:0018 e:000017 BLOCK  /Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor [FINISH]
c:0003 p:---- s:0015 e:000014 CFUNC  :catch
c:0002 p:0020 s:0010 e:000009 BLOCK  /Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor [FINISH]
c:0001 p:---- s:0003 e:000002 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:319:in `block in create_worker'
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:319:in `catch'
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:320:in `block (2 levels) in create_worker'
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:320:in `loop'
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:322:in `block (3 levels) in create_worker'
/Users/m/.rbenv/versions/2.5.5/lib/ruby/gems/2.5.0/gems/concurrent-ruby-1.1.5/lib/concurrent/executor/ruby_thread_pool_executor.rb:322:in `pop'

-- Machine register context ------------------------------------------------
 rax: 0x0000000000000000 rbx: 0x00007fe466262660 rcx: 0x0000000000010000
 rdx: 0x00007ffee6a5ad80 rdi: 0x000000010992aa38 rsi: 0x00007fe466262660
 rbp: 0x00007ffee6a5ad70 rsp: 0x00007ffee6a5ad38  r8: 0x0000000000000000
  r9: 0x000000000000800a r10: 0x0000000000000000 r11: 0xffffffff7f5896a8
 r12: 0x00007fe466262670 r13: 0x00007fff9f733f20 r14: 0x00007fff68fbbe30
 r15: 0x00007ffee6a5ad80 rip: 0x00007fff68fbbe34 rfl: 0x0000000000010206

-- C level backtrace information -------------------------------------------
0   ruby                                0x00000001093a4158 rb_vm_bugreport + 136
1   ruby                                0x000000010921a973 rb_bug_context + 467
2   ruby                                0x0000000109311e11 sigsegv + 81
3   libsystem_platform.dylib            0x00007fff68f98b5d _sigtramp + 29
4   libsystem_trace.dylib               0x00007fff68fbbe34 _os_log_cmp_key + 4

-- Other runtime information -----------------------------------------------

* Loaded script: rails_test

* Operating system:                macOS 10.14.5 (18F132)
* Ruby implementation:             Ruby 2.5.5p157
* `concurrent-ruby` version:       1.1.5
* `concurrent-ruby-ext` installed: no
* `concurrent-ruby-edge` used:     no

[cesarizu]

After some testing it seems that this commit is the culprit: eb81fff "avoid "can't be called from trap context" errors in ThreadLocalVar". Reverting that commit fixes the problem.

[pitr-ch]

Thank you for reporting and finding out the commit, it is a big help.

[rubenfonseca]

We're also seeing this problem with ruby-2.6.3.

[dmtask]

Same Problem here.

[pitr-ch]

I'll look into this as soon as possible.

[dmtask]

@pitr-ch Thank you. :)

[pitr-ch]

I do not have a reproducer, however, I've spotted potentially dangerous array access in the code which is fixed in #821, please try it and let me know if the issue goes away. Thanks.

[dmtask]

We were able to avoid the mistake and solved it differently. I still try to test the bugfix as fast as possible.

[pitr-ch]

Thank you @dmtask!

[dmtask]

For me, it works.

[davidw]

I am getting segfaults and some of them show this:

/home/davidw/.rvm/gems/ruby-2.6.4/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var.rb:87: [BUG] Segmentation fault at 0x000000002222000d
ruby 2.6.4p104 (2019-08-28 revision 67798) [x86_64-linux]

-- Control frame information -----------------------------------------------
c:0002 p:0006 s:0008 e:000006 BLOCK  /home/davidw/.rvm/gems/ruby-2.6.4/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var.rb:87 [FINISH]
c:0001 p:---- s:0003 e:000002 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
/home/davidw/.rvm/gems/ruby-2.6.4/gems/concurrent-ruby-1.1.5/lib/concurrent/atomic/ruby_thread_local_var.rb:87:in `block (2 levels) in threadlocal_finalizer'

-- Machine register context ------------------------------------------------
 RIP: 0x00007f53693d0dee RBP: 0x0000000000026ceb RSP: 0x00007f53604b97e8
 RAX: 0x0000561c4359b660 RBX: 0x0000561c3f79b0b0 RCX: 0x000000002222000d
 RDX: 0x0000000000000000 RDI: 0x0000561c4359b660 RSI: 0x0000561c44522a40
  R8: 0x0000561c3f625ce0  R9: 0x0000000000000004 R10: 0x0000561c44522a40
 R11: 0x0000000000000008 R12: 0x0000561c43916198 R13: 0x0000561c433f4180
 R14: 0x0000561c3f79b0c0 R15: 0x0000561c44522a40 EFL: 0x0000000000010202

-- C level backtrace information -------------------------------------------

I have a minimalistic Rails app that reproduces the problem, if that's helpful.

I tried applying the patch above, but it does not seem to fix it. I just hand-edited in to version 1.1.5, so I don't know if that's sufficient.