[pull] master from ruby:master#842
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pull[bot] merged 1 commit intoturkdevops:masterfrom Mar 11, 2026
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Patch 0837263 fixed a race condition on ubfs, but it's only valid if right after a call to `ubf_clear`, we assume the ubf function cannot be in the middle of running. This patch removes an optimization in `ubf_clear` that violates that assumption. In short, `ubf_clear` needs to take `th->interrupt_lock` unconditionally both to avoid deadlocks and to be able to reason about when ubfs can be run. This should fix CI errors like https://ci.rvm.jp/results/trunk-jemalloc@ruby-sp2-noble-docker/6242153. The error was in test_timeout.rb, which had a deadlock during VM shutdown. ```ruby r = Ractor.new do begin Timeout.timeout(0.1) { sleep } rescue Timeout::Error :ok end end.value assert_equal :ok, r ``` The deadlock happened during `rb_ractor_terminate_interrupt_main_thread` with 2 ractors: 1) r1 t1: UBF called with t2->interrupt_lock (ubf = ubf_waiting) 2) r2 t2: ubf cleared from previous thread_sched_wait_events_call (but no lock taken, because of optimization) 3) r2 t2: thread_sched_wait_events: acquire thread_sched_lock(t2) (caller calling native_sleep() in loop) 4) r2 t2: ubf_set: try to acquire t2->interrupt_lock [block] 5) r1 t1: try to acquire thread_sched_lock(t2) [block, deadlock] t2 needs to block on t2->interrupt_lock in step 2 until the ubf has completed. Only then can it register a new ubf in the next `native_sleep` iteration.
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