Mark an ISeq being JIT-ed

This is to avoid SEGV on a CC reference in a normal compilation
https://github.com/ruby/ruby/runs/1586578023

2 files changed, 15 insertions, 2 deletions

diff --git a/mjit.c b/mjit.c
index 1b0fc68ee7..d87961d7cc 100644
--- a/mjit.c
+++ b/mjit.c
@@ -935,8 +935,13 @@ mjit_finish(bool close_handle_p)
     verbose(1, "Successful MJIT finish");
 }
 
-// Called by rb_vm_mark() to mark active_units so that we do not GC ISeq which
-// may still be referred to by mjit_recompile() or compact_all_jit_code().
+// Called by rb_vm_mark().
+//
+// Mark an ISeq being compiled to prevent its CCs from being GC-ed, which
+// an MJIT worker may concurrently see.
+//
+// Also mark active_units so that we do not GC ISeq which may still be
+// referred to by mjit_recompile() or compact_all_jit_code().
 void
 mjit_mark(void)
 {
@@ -944,6 +949,9 @@ mjit_mark(void)
         return;
     RUBY_MARK_ENTER("mjit");
 
+    if (compiling_iseq != NULL)
+        rb_gc_mark((VALUE)compiling_iseq);
+
     // We need to release a lock when calling rb_gc_mark to avoid doubly acquiring
     // a lock by by mjit_gc_start_hook inside rb_gc_mark.
     //
diff --git a/mjit_worker.c b/mjit_worker.c
index 2096ea7bda..ba90cca7b6 100644
--- a/mjit_worker.c
+++ b/mjit_worker.c
@@ -1103,6 +1103,8 @@ compile_prelude(FILE *f)
 #endif
 }
 
+static rb_iseq_t *compiling_iseq = NULL;
+
 // Compile ISeq in UNIT and return function pointer of JIT-ed code.
 // It may return NOT_COMPILED_JIT_ISEQ_FUNC if something went wrong.
 static mjit_func_t
@@ -1136,6 +1138,8 @@ convert_unit_to_func(struct rb_mjit_unit *unit)
     }
     // We need to check again here because we could've waited on GC above
     in_jit = (unit->iseq != NULL);
+    if (in_jit)
+        compiling_iseq = unit->iseq;
     CRITICAL_SECTION_FINISH(3, "before mjit_compile to wait GC finish");
     if (!in_jit) {
         fclose(f);
@@ -1160,6 +1164,7 @@ convert_unit_to_func(struct rb_mjit_unit *unit)
 
     // release blocking mjit_gc_start_hook
     CRITICAL_SECTION_START(3, "after mjit_compile to wakeup client for GC");
+    compiling_iseq = NULL;
     in_jit = false;
     verbose(3, "Sending wakeup signal to client in a mjit-worker for GC");
     rb_native_cond_signal(&mjit_client_wakeup);