Avoid race condition manipulating heap when goroutine exits.

From-SVN: r170758

libgo/runtime/go-go.c

@@ -92,25 +92,32 @@ remove_current_thread (void)
   if (list_entry->next != NULL)
     list_entry->next->prev = list_entry->prev;
 
+  /* This will look runtime_mheap as needed.  */
   runtime_MCache_ReleaseAll (mcache);
 
+  /* This should never deadlock--there shouldn't be any code that
+     holds the runtime_mheap lock when locking __go_thread_ids_lock.
+     We don't want to do this after releasing __go_thread_ids_lock
+     because it will mean that the garbage collector might run, and
+     the garbage collector does not try to lock runtime_mheap in all
+     cases since it knows it is running single-threaded.  */
+  runtime_lock (&runtime_mheap);
+  mstats.heap_alloc += mcache->local_alloc;
+  mstats.heap_objects += mcache->local_objects;
+  __builtin_memset (mcache, 0, sizeof (struct MCache));
+  runtime_FixAlloc_Free (&runtime_mheap.cachealloc, mcache);
+  runtime_unlock (&runtime_mheap);
+
   /* As soon as we release this look, a GC could run.  Since this
      thread is no longer on the list, the GC will not find our M
      structure, so it could get freed at any time.  That means that
-     any code from here to thread exit must not assume that the m is
+     any code from here to thread exit must not assume that m is
      valid.  */
   m = NULL;
 
   i = pthread_mutex_unlock (&__go_thread_ids_lock);
   __go_assert (i == 0);
 
-  runtime_lock (&runtime_mheap);
-  mstats.heap_alloc += mcache->local_alloc;
-  mstats.heap_objects += mcache->local_objects;
-  __builtin_memset (mcache, 0, sizeof (struct MCache));
-  runtime_FixAlloc_Free (&runtime_mheap.cachealloc, mcache);
-  runtime_unlock (&runtime_mheap);
-
   free (list_entry);
 }