Merge rev 38770 from 3.4 branch.

tpc_abort():  Release the commit lock no matter what.

NEWS.txt

@@ -38,6 +38,14 @@ ZEO
   erroneous ``AttributeError`` exception.  Thanks to Tres Seaver for the
   diagnosis.
 
+BaseStorage
+-----------
+
+- (3.6a4) Nothing done by ``tpc_abort()`` should raise an exception.
+  However, if something does (an error case), ``BaseStorage.tpc_abort()``
+  left the commit lock in the acquired state, causing any later attempt
+  to commit changes hang.
+
 PersistentMapping
 -----------------
 

src/ZODB/BaseStorage.py

@@ -192,8 +192,8 @@ class BaseStorage(UndoLogCompatible):
             self._abort()
             self._clear_temp()
             self._transaction = None
-            self._commit_lock_release()
         finally:
+            self._commit_lock_release()
             self._lock_release()
 
     def _abort(self):