Bug#25289 - repair table causes "my_seek.c:56:

            my_seek: Assertion `fd != -1' failed"

In difficult optimize/repair situations the server could crash.
Under some circumstances the server retries an optimize/repair
with more elaborate options. But it did not check if the first
attempt failed so badly that a second one must not be tried.

This could happen when a new data file has been created
but it was not possible to open it. In this case the
repair leaves behind a table with closed data file.
This must not be used for another repair attempt.

We do now detect the closed data file and do not try
another repair attempt in this situation.

No test case. The required table corruption can not be
repeated easily. There is a test program attached to
bug 25433.

sql/ha_myisam.cc

@@ -867,6 +867,22 @@ int ha_myisam::repair(THD *thd, MI_CHECK &param, bool optimize)
   ha_rows rows= file->state->records;
   DBUG_ENTER("ha_myisam::repair");
 
+  /*
+    Normally this method is entered with a properly opened table. If the
+    repair fails, it can be repeated with more elaborate options. Under
+    special circumstances it can happen that a repair fails so that it
+    closed the data file and cannot re-open it. In this case file->dfile
+    is set to -1. We must not try another repair without an open data
+    file. (Bug #25289)
+  */
+  if (file->dfile == -1)
+  {
+    sql_print_information("Retrying repair of: '%s' failed. "
+                          "Please try REPAIR EXTENDED or myisamchk",
+                          table->path);
+    DBUG_RETURN(HA_ADMIN_FAILED);
+  }
+
   param.db_name    = table->table_cache_key;
   param.table_name = table->table_name;
   param.tmpfile_createflag = O_RDWR | O_TRUNC;