Bug#12845 - Stress test: Server crashes on CREATE .. SELECT statement

Solution for 5.0.
Changed calls to open_table(). Requested to ignore
flush at places where the command did already lock tables.
This could happen in CREATE ... SELECT and ALTER TABLE.

No test case. The bug can only be triggered by true concurrency.
The stress test suite provides a test case for this.

sql/sql_base.cc

@@ -1030,23 +1030,23 @@ TABLE *reopen_name_locked_table(THD* thd, TABLE_LIST* table_list)
 
   SYNOPSIS
     open_table()
-      thd         Thread context
-      table_list  Open first table in list
-      refresh     Pointer to memory that will be set to 1 if
-                  we need to close all tables and reopen them
-                  If this is a NULL pointer, then the is no version
-                  number checking and the table is not put in the
-                  thread-open-list
-      flags       Bitmap of flags to modify how open works:
-                    MYSQL_LOCK_IGNORE_FLUSH - Open table even if someone
-                    has done a flush or namelock on it.
+    thd                 Thread context.
+    table_list          Open first table in list.
+    refresh      INOUT  Pointer to memory that will be set to 1 if
+                        we need to close all tables and reopen them.
+                        If this is a NULL pointer, then the table is not
+                        put in the thread-open-list.
+    flags               Bitmap of flags to modify how open works:
+                          MYSQL_LOCK_IGNORE_FLUSH - Open table even if
+                          someone has done a flush or namelock on it.
+                          No version number checking is done.
 
   IMPLEMENTATION
     Uses a cache of open tables to find a table not in use.
 
   RETURN
     NULL  Open failed.  If refresh is set then one should close
-          all other tables and retry the open
+          all other tables and retry the open.
     #     Success. Pointer to TABLE object for open table.
 */
 
@@ -1201,10 +1201,12 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
 
   if (!thd->open_tables)
     thd->version=refresh_version;
-  else if (thd->version != refresh_version && refresh)
+  else if ((thd->version != refresh_version) &&
+           ! (flags & MYSQL_LOCK_IGNORE_FLUSH))
   {
     /* Someone did a refresh while thread was opening tables */
-    *refresh=1;
+    if (refresh)
+      *refresh=1;
     VOID(pthread_mutex_unlock(&LOCK_open));
     DBUG_RETURN(0);
   }

sql/sql_table.cc

@@ -1756,7 +1756,8 @@ TABLE *create_table_from_items(THD *thd, HA_CREATE_INFO *create_info,
                             create_info, *extra_fields, *keys, 0,
                             select_field_count))
     {
-      if (!(table= open_table(thd, create_table, thd->mem_root, (bool*)0, 0)))
+      if (! (table= open_table(thd, create_table, thd->mem_root, (bool*) 0,
+                               MYSQL_LOCK_IGNORE_FLUSH)))
         quick_rm_table(create_info->db_type, create_table->db,
                        table_case_name(create_info, create_table->table_name));
     }
@@ -3579,7 +3580,8 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
       bzero((void*) &tbl, sizeof(tbl));
       tbl.db= new_db;
       tbl.table_name= tbl.alias= tmp_name;
-      new_table= open_table(thd, &tbl, thd->mem_root, 0, 0);
+      new_table= open_table(thd, &tbl, thd->mem_root, (bool*) 0,
+                            MYSQL_LOCK_IGNORE_FLUSH);
     }
     else
     {