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From:Davi Arnaut Date:October 6 2007 4:22am
Subject:bk commit into 5.0 tree (davi:1.2528) BUG#31409
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ChangeSet@stripped, 2007-10-06 01:21:55-03:00, davi@stripped +2 -0
  Bug#31409 RENAME TABLE causes server crash or deadlock when used with HANDLER statements
  This deadlock occurs when a client issues a HANDLER ... OPEN statement
  that tries to open a table that has a pending name-lock on it by another
  client that also needs a name-lock on some other table which is already
  open and associated to a HANDLER instance owned by the first client.
  The deadlock happens because the open_table() function will back-off
  and wait until the name-lock goes away, causing a circular wait if some
  other name-lock is also pending for one of the open HANDLER tables.
  Such situation, for example, can be easily repeated by issuing a RENAME
  TABLE command in such a way that the existing table is already open
  as a HANDLER table by another client and this client tries to open
  a HANDLER to the new table name.
  The solution is to allow handler tables with older versions (makred for
  flush) to be closed before waiting for the name-lock completion. This is
  safe because no other name-lock can be issued between the flush and the
  check for pending name-locks.
  The test case for this bug is going to be committed into 5.1 because it
  requires a test feature only avaiable in 5.1 (wait_condition).

  sql/, 2007-10-06 01:21:52-03:00, davi@stripped +8 -2
    Improve comments in the open_table() function, stating the importance
    of the handler tables flushing for the back-off process.

  sql/, 2007-10-06 01:21:53-03:00, davi@stripped +28 -19
    Allows handler tables flushes when opening new tables in order to avoid
    potential deadlocks. Add comments explaining the importance of the flush.

diff -Nrup a/sql/ b/sql/
--- a/sql/	2007-08-24 08:28:10 -03:00
+++ b/sql/	2007-10-06 01:21:52 -03:00
@@ -1745,7 +1745,12 @@ TABLE *open_table(THD *thd, TABLE_LIST *
-  /* close handler tables which are marked for flush */
+  /*
+    In order for the back off and re-start process to work properly, the
+    handler tables which are marked for flush (with older versions) MUST
+    be closed. This is specially important if a name-lock is pending for
+    any table of the handler_tables list, otherwise a deadlock may occur.
+  */
   if (thd->handler_tables)
     mysql_ha_flush(thd, (TABLE_LIST*) NULL, MYSQL_HA_REOPEN_ON_USAGE, TRUE);
@@ -1809,7 +1814,8 @@ TABLE *open_table(THD *thd, TABLE_LIST *
         table->s->version (this is an optimization (?)).
         table->db_stat == 0 signals wait_for_locked_table_names
         that the tables in question are not used any more. See
-        table_is_used call for details.
+        table_is_used call for details. Stale HANDLER tables were
+        already closed under this same critical section.
diff -Nrup a/sql/ b/sql/
--- a/sql/	2007-10-04 17:34:38 -03:00
+++ b/sql/	2007-10-06 01:21:53 -03:00
@@ -182,7 +182,7 @@ bool mysql_ha_open(THD *thd, TABLE_LIST 
   char          *db, *name, *alias;
   uint          dblen, namelen, aliaslen, counter;
   int           error;
-  TABLE         *backup_open_tables, *backup_handler_tables;
+  TABLE         *backup_open_tables;
   DBUG_PRINT("enter",("'%s'.'%s' as '%s'  reopen: %d",
                       tables->db, tables->table_name, tables->alias,
@@ -211,14 +211,20 @@ bool mysql_ha_open(THD *thd, TABLE_LIST 
-  /* save open_ and handler_ tables state */
-  backup_open_tables= thd->open_tables;
-  backup_handler_tables= thd->handler_tables;
+  /*
+    Save and reset the open_tables list so that open_tables() won't
+    be able to access (or know about) the previous list. And on return
+    from open_tables(), thd->open_tables will contain only the opened
+    table.
+    The thd->handler_tables list is kept as-is to avoid deadlocks if
+    open_table(), called by open_tables(), needs to back-off because
+    of a pending name-lock on the table being opened.
-  /* no pre-opened tables */
+    See open_table() back-off comments for more details.
+  */
+  backup_open_tables= thd->open_tables;
   thd->open_tables= NULL;
-  /* to avoid flushes */
-  thd->handler_tables= NULL;
     open_tables() will set 'tables->table' if successful.
@@ -231,9 +237,12 @@ bool mysql_ha_open(THD *thd, TABLE_LIST 
   error= open_tables(thd, &tables, &counter, 0);
   /* restore the state and merge the opened table into handler_tables list */
-  thd->handler_tables= thd->open_tables ?
-                       thd->open_tables->next= backup_handler_tables,
-                       thd->open_tables : backup_handler_tables;
+  if (thd->open_tables)
+  {
+    thd->open_tables->next= thd->handler_tables;
+    thd->handler_tables= thd->open_tables;
+  }
   thd->open_tables= backup_open_tables;
   if (error)
@@ -360,7 +369,7 @@ bool mysql_ha_read(THD *thd, TABLE_LIST 
                    ha_rows select_limit_cnt, ha_rows offset_limit_cnt)
   TABLE_LIST    *hash_tables;
-  TABLE         *table, *backup_open_tables, *backup_handler_tables;
+  TABLE         *table, *backup_open_tables;
   MYSQL_LOCK    *lock;
   List<Item>	list;
   Protocol	*protocol= thd->protocol;
@@ -437,20 +446,20 @@ retry:
-  /* save open_ and handler_ tables state */
+  /* save open_tables state */
   backup_open_tables= thd->open_tables;
-  backup_handler_tables= thd->handler_tables;
-  /* no pre-opened tables */
-  thd->open_tables= NULL;
-  /* to avoid flushes */
-  thd->handler_tables= NULL;
+  /* not only temporary tables */
+  thd->open_tables= thd->handler_tables;
+  /*
+    Lock table, but if it fails don't close any tables. That's why the
+    thd->handler_table list is not protected here, mysql_lock_tables
+    won't touch it.
+  */
   lock= mysql_lock_tables(thd, &tables->table, 1,
                           MYSQL_LOCK_NOTIFY_IF_NEED_REOPEN, &need_reopen);
   /* restore previous context */
-  thd->handler_tables= backup_handler_tables;
   thd->open_tables= backup_open_tables;
   if (need_reopen)
bk commit into 5.0 tree (davi:1.2528) BUG#31409Davi Arnaut6 Oct