Lock finalizers lists at exit (#49931)

Author: kpamnany

src/gc.c

@@ -526,12 +526,17 @@ void jl_gc_run_all_finalizers(jl_task_t *ct)
     jl_ptls_t* gc_all_tls_states;
     gc_n_threads = jl_atomic_load_acquire(&jl_n_threads);
     gc_all_tls_states = jl_atomic_load_relaxed(&jl_all_tls_states);
+    // this is called from `jl_atexit_hook`; threads could still be running
+    // so we have to guard the finalizers' lists
+    JL_LOCK_NOGC(&finalizers_lock);
     schedule_all_finalizers(&finalizer_list_marked);
     for (int i = 0; i < gc_n_threads; i++) {
         jl_ptls_t ptls2 = gc_all_tls_states[i];
         if (ptls2 != NULL)
             schedule_all_finalizers(&ptls2->finalizers);
     }
+    // unlock here because `run_finalizers` locks this
+    JL_UNLOCK_NOGC(&finalizers_lock);
     gc_n_threads = 0;
     gc_all_tls_states = NULL;
     run_finalizers(ct);