Issue #20016 has been updated by jhawthorn (John Hawthorn). I opened a PR with a proposal to fix this. https://github.com/ruby/ruby/pull/9311 The issue is that under M:N threads `rb_vm_main_ractor_ec` now returns NULL when all threads in the main Ractor's shared thread are sleeping. rb_postponed_job_register_one needs to always be able to find _a_ working EC. ---------------------------------------- Bug #20016: 3.3.0dev `rb_postponed_job_register_one` crashes when `RUBY_MN_THREADS=1` https://bugs.ruby-lang.org/issues/20016#change-105775 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal * Assignee: ko1 (Koichi Sasada) * ruby -v: ruby 3.3.0dev (2023-11-22T17:01:13Z shopify c1fc1a00ea) +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: ``` [BUG] Segmentation fault at 0x0000000000000020 ruby 3.3.0dev (2023-11-22T17:01:13Z shopify c1fc1a00ea) +MN [x86_64-linux] -- Machine register context ------------------------------------------------ RIP: 0x000055df5fe38489 RBP: 0x00007f517bc59000 RSP: 0x00007f5123f3c6d0 RAX: 0x0000000000000000 RBX: 0x00007f51596554e0 RCX: 0x00007f517bdb6b40 RDX: 0x0000000000000001 RDI: 0x00007f517bc59000 RSI: 0x0000000000000000 R8: 0x0000000000000000 R9: 0x00000000ffffffff R10: 0x0000000000000000 R11: 0x0000000000000246 R12: 0x0000000000000000 R13: 0x0000000000000000 R14: 0x0000000000001ea5 R15: 0x00007f517bc59104 EFL: 0x0000000000010202 -- C level backtrace information ------------------------------------------- /usr/local/ruby/bin/ruby(rb_print_backtrace+0x14) [0x55df5fe328e1] /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_dump.c:812 /usr/local/ruby/bin/ruby(rb_vm_bugreport) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_dump.c:1143 /usr/local/ruby/bin/ruby(rb_bug_for_fatal_signal+0xfc) [0x55df5ffe509c] /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/error.c:1065 /usr/local/ruby/bin/ruby(sigsegv+0x4d) [0x55df5fd7f19d] /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/signal.c:920 /lib/x86_64-linux-gnu/libc.so.6(0x7f517c277520) [0x7f517c277520] /usr/local/ruby/bin/ruby(rbimpl_atomic_or+0x0) [0x55df5fe38489] /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_trace.c:1691 /usr/local/ruby/bin/ruby(postponed_job_register) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_trace.c:1693 /usr/local/ruby/bin/ruby(postponed_job_register) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_trace.c:1675 /usr/local/ruby/bin/ruby(rb_postponed_job_register_one) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/vm_trace.c:1746 /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/lib/stackprof/stackprof.so(stackprof_signal_handler+0x2d) [0x7f5159655434] /tmp/bundle/ruby/3.3.0+0/gems/stackprof-0.2.25/ext/stackprof/stackprof.c:763 /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(0x7f517c277520) [0x7f517c277520] /lib/x86_64-linux-gnu/libc.so.6(0x7f517c2c6117) [0x7f517c2c6117] /lib/x86_64-linux-gnu/libc.so.6(pthread_cond_wait+0x211) [0x7f517c2c8a41] /usr/local/ruby/bin/ruby(rb_native_cond_wait+0xb) [0x55df5fdc75fb] /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/thread_pthread.c:214 /usr/local/ruby/bin/ruby(ractor_sched_deq) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/thread_pthread.c:1230 /usr/local/ruby/bin/ruby(nt_start) /tmp/ruby-build/ruby-3.3.0-c1fc1a00ea9633961153451d0e927db49c1b268d/thread_pthread.c:2209 /lib/x86_64-linux-gnu/libc.so.6(0x7f517c2c9ac3) [0x7f517c2c9ac3] ``` Ref: https://github.com/tmm1/stackprof/issues/221 -- https://bugs.ruby-lang.org/