Propagate crash of GC thread to mutator thread

This allows the mutator thread to dump its backtrace when a GC thread crashes.

Author: peterzhu2118

gc/mmtk/mmtk.c

@@ -38,6 +38,11 @@ struct objspace {
     pthread_cond_t cond_world_started;
     size_t start_the_world_count;
 
+    struct {
+        bool gc_thread_crashed;
+        char crash_msg[256];
+    } crash_context;
+
     struct rb_gc_vm_context vm_context;
 
     unsigned int fork_hook_vm_lock_lev;
@@ -169,6 +174,10 @@ rb_mmtk_block_for_gc(MMTk_VMMutatorThread mutator)
             pthread_cond_wait(&objspace->cond_world_started, &objspace->mutex);
         }
 
+        if (RB_UNLIKELY(objspace->crash_context.gc_thread_crashed)) {
+            rb_bug("%s", objspace->crash_context.crash_msg);
+        }
+
         if (objspace->measure_gc_time) {
             struct timespec gc_end_time;
             clock_gettime(CLOCK_MONOTONIC, &gc_end_time);
@@ -424,6 +433,32 @@ rb_mmtk_special_const_p(MMTk_ObjectReference object)
     return RB_SPECIAL_CONST_P(obj);
 }
 
+RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 1, 2)
+static void
+rb_mmtk_gc_thread_bug(const char *msg, ...)
+{
+    struct objspace *objspace = rb_gc_get_objspace();
+
+    objspace->crash_context.gc_thread_crashed = true;
+
+    va_list args;
+    va_start(args, msg);
+    vsnprintf(objspace->crash_context.crash_msg, sizeof(objspace->crash_context.crash_msg), msg, args);
+    va_end(args);
+
+    rb_mmtk_resume_mutators();
+
+    sleep(5);
+
+    rb_bug("rb_mmtk_gc_thread_bug");
+}
+
+static void
+rb_mmtk_gc_thread_panic_handler(void)
+{
+    rb_mmtk_gc_thread_bug("MMTk GC thread panicked");
+}
+
 static void
 rb_mmtk_mutator_thread_panic_handler(void)
 {
@@ -454,6 +489,7 @@ MMTk_RubyUpcalls ruby_upcalls = {
     rb_mmtk_update_finalizer_table,
     rb_mmtk_special_const_p,
     rb_mmtk_mutator_thread_panic_handler,
+    rb_mmtk_gc_thread_panic_handler,
 };
 
 // Use max 80% of the available memory by default for MMTk

gc/mmtk/mmtk.h

@@ -79,6 +79,7 @@ typedef struct MMTk_RubyUpcalls {
     void (*update_finalizer_table)(void);
     bool (*special_const_p)(MMTk_ObjectReference object);
     void (*mutator_thread_panic_handler)(void);
+    void (*gc_thread_panic_handler)(void);
 } MMTk_RubyUpcalls;
 
 typedef struct MMTk_RawVecOfObjRef {

gc/mmtk/src/abi.rs

@@ -323,6 +323,7 @@ pub struct RubyUpcalls {
     pub update_finalizer_table: extern "C" fn(),
     pub special_const_p: extern "C" fn(object: ObjectReference) -> bool,
     pub mutator_thread_panic_handler: extern "C" fn(),
+    pub gc_thread_panic_handler: extern "C" fn(),
 }
 
 unsafe impl Sync for RubyUpcalls {}

gc/mmtk/src/lib.rs

@@ -126,8 +126,6 @@ fn handle_gc_thread_panic(panic_info: &PanicHookInfo) {
             eprintln!("Unknown backtrace status: {s:?}");
         }
     }
-
-    std::process::abort();
 }
 
 pub(crate) fn set_panic_hook() {
@@ -140,6 +138,8 @@ pub(crate) fn set_panic_hook() {
     std::panic::set_hook(Box::new(move |panic_info| {
         if is_gc_thread(std::thread::current().id()) {
             handle_gc_thread_panic(panic_info);
+
+            (crate::binding().upcalls().gc_thread_panic_handler)();
         } else {
             old_hook(panic_info);
             (crate::MUTATOR_THREAD_PANIC_HANDLER