fix

---
 gdb/defs.h        |  3 +++
 gdb/dwarf2/read.h | 22 ++++++++++++++--------
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/gdb/defs.h b/gdb/defs.h
index 19f379d6588..c129bf633a1 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -235,6 +235,9 @@ gdb_static_assert (nr_languages <= (1 << LANGUAGE_BITS));
 /* The number of bytes needed to represent all languages.  */
 #define LANGUAGE_BYTES ((LANGUAGE_BITS + HOST_CHAR_BIT - 1) / HOST_CHAR_BIT)
 
+#define LANGUAGE_CONTAINER unsigned char
+gdb_static_assert (sizeof (LANGUAGE_CONTAINER) >= LANGUAGE_BYTES);
+
 enum precision_type
   {
     single_precision,
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index f98d8b27649..f4362fe3ede 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -108,6 +108,7 @@ struct dwarf2_per_cu_data
       m_header_read_in (false),
       mark (false),
       files_read (false),
+      m_lang (language_unknown),
       scanned (false)
   {
   }
@@ -180,7 +181,7 @@ struct dwarf2_per_cu_data
   packed<dwarf_unit_type, 1> m_unit_type = (dwarf_unit_type) 0;
 
   /* The language of this CU.  */
-  packed<language, LANGUAGE_BYTES> m_lang = language_unknown;
+  std::atomic<LANGUAGE_CONTAINER> m_lang;
 
 public:
   /* True if this CU has been scanned by the indexer; false if
@@ -326,17 +327,22 @@ struct dwarf2_per_cu_data
 
   enum language lang () const
   {
-    gdb_assert (m_lang != language_unknown);
-    return m_lang;
+    LANGUAGE_CONTAINER lc = m_lang;
+    enum language l = (enum language)lc;
+    gdb_assert (l != language_unknown);
+    return l;
   }
 
   void set_lang (enum language lang)
   {
-    /* We'd like to be more strict here, similar to what is done in
-       set_unit_type,  but currently a partial unit can go from unknown to
-       minimal to ada to c.  */
-    if (m_lang != lang)
-      m_lang = lang;
+    LANGUAGE_CONTAINER lc = (LANGUAGE_CONTAINER)lang;
+    LANGUAGE_CONTAINER nope = (LANGUAGE_CONTAINER)language_unknown;
+    if (m_lang.compare_exchange_strong (nope, lc))
+      return;
+    nope = lang;
+    if (m_lang.compare_exchange_strong (nope, lc))
+      return;
+    gdb_assert_not_reached ();
   }
 
   /* Free any cached file names.  */