Bug#16757869: INNODB: POSSIBLE REGRESSION IN 5.5.31, BUG#16004999

The problem was that if UPDATE with subselect caused a
deadlock inside InnoDB, this deadlock was not properly
handled by the SQL layer. This meant that the SQL layer
would try to unlock the row after InnoDB had rolled
back the transaction. This caused an assertion inside
InnoDB.
  
This patch fixes the problem by checking for errors
reported by SQL_SELECT::skip_record() and not calling
unlock_row() if any errors have been reported.

This bug is similar to Bug#13586591, but for UPDATE
rather than DELETE. Similar issues in filesort/opt_range/
sql_select will be investigated and handled in the scope
of Bug#16767929

sql/sql_update.cc

-/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -555,7 +555,10 @@ int mysql_update(THD *thd,
         if (select && select->skip_record(thd, &skip_record))
         {
           error= 1;
-          table->file->unlock_row();
+          /*
+            Don't try unlocking the row if skip_record reported an error since
+            in this case the transaction might have been rolled back already.
+          */
           break;
         }
         if (!skip_record)
@@ -801,8 +804,17 @@ int mysql_update(THD *thd,
         }
       }
     }
-    else
+    /*
+      Don't try unlocking the row if skip_record reported an error since in
+      this case the transaction might have been rolled back already.
+    */
+    else if (!thd->is_error())
       table->file->unlock_row();
+    else
+    {
+      error= 1;
+      break;
+    }
     thd->warning_info->inc_current_row_for_warning();
     if (thd->is_error())
     {