[ruby-core:114026] [Ruby master Bug#18464] RUBY_INTERNAL_EVENT_NEWOBJ tracepoint causes an interpreter crash when combined with Ractors

Issue #18464 has been updated by ivoanjo (Ivo Anjo).


Thanks again @nagachika!

Can I bother you with a backport to 3.0 as well? I know that one is getting "long in the tooth" in terms of support, but having it fixed would mean this crash would not happen on any of the Ruby releases which support Ractors (3.0/3.1/3.2/...) which would make our usage of tracepoints in the ddtrace gem simpler :)

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Bug #18464: RUBY_INTERNAL_EVENT_NEWOBJ tracepoint causes an interpreter crash when combined with Ractors
https://bugs.ruby-lang.org/issues/18464#change-103689

* Author: kjtsanaktsidis (KJ Tsanaktsidis)
* Status: Closed
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* ruby -v: ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin20]
* Backport: 2.6: DONTNEED, 2.7: DONTNEED, 3.0: REQUIRED, 3.1: DONE, 3.2: DONE
----------------------------------------
When a Ractor is created whilst a tracepoint for `RUBY_INTERNAL_EVENT_NEWOBJ` is active (registered with `rb_tracepoint_new`/`rb_tracepoint_enabled`), the interpreter crashes with a null pointer dereference with the following backtrace:

```
[BUG] Segmentation fault at 0x0000000000000000
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin20]

...

-- C level backtrace information -------------------------------------------
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_print_backtrace+0xf) [0x10a15fadd] vm_dump.c:759
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_vm_bugreport) vm_dump.c:1045
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_vm_bugreport) (null):0
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(bug_report_end+0x0) [0x109f96b81] error.c:820
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_bug_for_fatal_signal) error.c:820
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(sigsegv+0x52) [0x10a0be3a2] signal.c:964
/usr/lib/system/libsystem_platform.dylib(_sigtramp+0x1d) [0x7fff20934d7d]
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(gc_event_hook_body+0x4) [0x109fb9d21] gc.c:2214
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(newobj_slowpath) gc.c:2486
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(newobj_slowpath_wb_unprotected) gc.c:2507
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(newobj_fill+0x0) [0x109fac92e] gc.c:2543
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(newobj_of0) gc.c:2553
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(newobj_of) gc.c:2552
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_wb_unprotected_newobj_of) gc.c:2567
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(io_alloc+0x12) [0x109fd341c] io.c:1047
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(prep_io) io.c:8483
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(prep_stdio) io.c:8514
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_io_prep_stdin) io.c:8532
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(thread_start_func_2+0xf7) [0x10a1058a7] thread.c:802
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(rb_native_cond_initialize+0x0) [0x10a1055fb] ./thread_pthread.c:1047
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(register_cached_thread_and_wait) ./thread_pthread.c:1099
/Users/ktsanaktsidis/Code/zendesk/ruby/ruby(thread_start_func_1) ./thread_pthread.c:1054
/usr/lib/system/libsystem_pthread.dylib(_pthread_start+0xe0) [0x7fff208ef8fc]

```

(full output is attached). 

This seems to be because the new Ractor sets up stdio objects (`rb_io_prep_stdin` et. al.), which in turn allocate Ruby objects, before `rb_ec_initialize_vm_stack` is called to set up the initial stack frame.

I've attached a patch which works around this by not firing GC event hooks if there is no control frame on the execution context. The patch also includes a test which reproduces the issue using the `objspace` extension; creating a Ractor within an `ObjectSpace.trace_object_allocations` block is enough to trigger the crash. The patch seems to fix things, but if you folk prefer I can also try swapping around the order of `prep_stdio` and `rb_ec_initialize_vm_stack`.


---Files--------------------------------
0001-Fix-interpreter-crash-caused-by-RUBY_INTERNAL_EVENT_.patch (1.91 KB)
crash.log (26.1 KB)
ruby_2022-01-08-151326_8927-ktsanaktsidis.crash (18.8 KB)


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