From: "byroot (Jean Boussier) via ruby-core" <ruby-core@...>
Date: 2023-11-22T17:55:23+00:00
Subject: [ruby-core:115459] [Ruby master Bug#20017] 3.3.0dev `rb_thread_profile_frames` crashes when `RUBY_MN_THREADS=1`

Issue #20017 has been reported by byroot (Jean Boussier).

----------------------------------------
Bug #20017: 3.3.0dev `rb_thread_profile_frames` crashes when `RUBY_MN_THREADS=1`
https://bugs.ruby-lang.org/issues/20017

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.3.0dev (2023-11-19T03:01:05Z shopify 9aee12cc28) +MN [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
I discovered this while running our internal CI with MaNy enabled, our application crash when trying to profile with StackProf (with postponed jobs disabled):

```
[BUG] Segmentation fault at 0x0000000000000010
ruby 3.3.0dev (2023-11-19T03:01:05Z shopify 9aee12cc28) +MN [x86_64-linux]

-- C level backtrace information -------------------------------------------
/usr/local/ruby/bin/ruby(rb_print_backtrace+0x14) [0x55c8f16333e1] /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/vm_dump.c:812
/usr/local/ruby/bin/ruby(rb_vm_bugreport) /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/vm_dump.c:1143
/usr/local/ruby/bin/ruby(rb_bug_for_fatal_signal+0xfc) [0x55c8f17e559c] /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/error.c:1065
/usr/local/ruby/bin/ruby(sigsegv+0x4d) [0x55c8f158091d] /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/signal.c:920
/lib/x86_64-linux-gnu/libc.so.6(0x7ff3db333520) [0x7ff3db333520]
/usr/local/ruby/bin/ruby(thread_profile_frames+0x10) [0x55c8f162efd0] /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/vm_backtrace.c:1587
/tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_buffer_sample+0x28) [0x7ff3b7d2435c] /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/ext/stackprof/stackprof.c:622
/tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_buffer_sample) /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/ext/stackprof/stackprof.c:604
/tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_buffer_sample) (null):0
/tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_signal_handler+0x5) [0x7ff3b7d24545] /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/ext/stackprof/stackprof.c:767
/tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_signal_handler) /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/ext/stackprof/stackprof.c:722
/lib/x86_64-linux-gnu/libc.so.6(0x7ff3db333520) [0x7ff3db333520]
/lib/x86_64-linux-gnu/libc.so.6(pthread_cond_wait+0x24a) [0x7ff3db384a7a]
/usr/local/ruby/bin/ruby(rb_native_cond_wait+0xb) [0x55c8f15c8cbb] /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/thread_pthread.c:214
/usr/local/ruby/bin/ruby(ractor_sched_deq) /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/thread_pthread.c:1230
/usr/local/ruby/bin/ruby(nt_start) /tmp/ruby-build/ruby-3.3.0-9aee12cc28cbca40306784e54e38558688caa9f7/thread_pthread.c:2209
```

For additional context, as far as I know `rb_thread_profile_frames` isn't officially async signal safe, but it happens to be since 3.0 for the interpreter, and 3.3 for YJIT, so StackProf tries not to use postponed jobs for profiling when it can as it leads to much more accurate profiling results.

Ref: https://github.com/tmm1/stackprof/issues/221 



-- 
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