merge revision(s) 86c262541ad07528842d76dab4b9b34bd888d5f4,7e14762159643b4415e094f9d2a90afaf7994588: [Backport #17935]

	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.
	---
	 mjit.c        | 21 +++++++++++++--------
	 mjit_worker.c |  4 ++++
	 2 files changed, 17 insertions(+), 8 deletions(-)

	Do not doubly hold an MJIT lock

	This is a follow-up of 86c262541ad07528842d76dab4b9b34bd888d5f4.
	CRITICAL_SECTION_START/FINISH are not needed when it's called from an
	MJIT worker.

	Also, ZALLOC needs to be calloc because ZALLOC may trigger GC, which an
	MJIT worker must not do.
	---
	 mjit.c        | 23 ++++++++++++++---------
	 mjit_worker.c |  4 ++--
	 2 files changed, 16 insertions(+), 11 deletions(-)

1 files changed, 4 insertions, 0 deletions

diff --git a/mjit_worker.c b/mjit_worker.c
index ad36ec6151..e2db644c92 100644
--- a/mjit_worker.c
+++ b/mjit_worker.c
@@ -1402,6 +1402,8 @@ unload_units(void)
     }
 }
 
+static void mjit_add_iseq_to_process(const rb_iseq_t *iseq, const struct rb_mjit_compile_info *compile_info, bool worker_p);
+
 // 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.
@@ -1451,6 +1453,8 @@ 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, true);
                     }
                 }
             }