Fix a race condition around mjit_recompile

This fixes SEGVs like https://github.com/ruby/ruby/runs/2715166621?check_suite_focus=true.

When mjit_recompile is called when mjit_compile is compiling the exact
same iseq (and after it called mjit_capture_cc_entries), iseq->body->jit_unit
is re-created and its cc_entries becomes NULL. Then, when it tries to
lookup cc_entries through iseq->body->jit_unit, it fails.

1 files changed, 4 insertions, 0 deletions

diff --git a/mjit_worker.c b/mjit_worker.c
index 3a73f14679..50f1b0787e 100644
--- a/mjit_worker.c
+++ b/mjit_worker.c
@@ -1396,6 +1396,8 @@ unload_units(void)
     }
 }
 
+static void mjit_add_iseq_to_process(const rb_iseq_t *iseq, const struct rb_mjit_compile_info *compile_info);
+
 // The function implementing a worker. It is executed in a separate
 // thread by rb_thread_create_mjit_thread. It compiles precompiled header
 // and then compiles requested ISeqs.
@@ -1445,6 +1447,8 @@ mjit_worker(void)
                         unit->stale_p = false;
                         remove_from_list(unit, &active_units);
                         add_to_list(unit, &stale_units);
+                        // Lazily put it to unit_queue as well to avoid race conditions on jit_unit with mjit_compile.
+                        mjit_add_iseq_to_process(unit->iseq, &unit->iseq->body->jit_unit->compile_info);
                     }
                 }
             }