Bug#16986 - Deadlock condition with MyISAM tables

Addendum fixes after changing the condition variable
for the global read lock.

The stress test suite revealed some deadlocks. Some were
related to the new condition variable (COND_global_read_lock)
and some were general problems with the global read lock.

It is now necessary to signal COND_global_read_lock whenever 
COND_refresh is signalled.

We need to wait for the release of a global read lock if one 
is set before every operation that requires a write lock.
But we must not wait if we have locked tables by LOCK TABLES.
After setting a global read lock a thread waits until all
write locks are released.

mysql-test/r/lock_multi.result

@@ -67,6 +67,21 @@ Select_priv
 N
 use test;
 use test;
+CREATE TABLE t1 (c1 int);
+LOCK TABLE t1 WRITE;
+ FLUSH TABLES WITH READ LOCK;
+CREATE TABLE t2 (c1 int);
+UNLOCK TABLES;
+UNLOCK TABLES;
+DROP TABLE t1, t2;
+CREATE TABLE t1 (c1 int);
+LOCK TABLE t1 WRITE;
+ FLUSH TABLES WITH READ LOCK;
+CREATE TABLE t2 AS SELECT * FROM t1;
+ERROR HY000: Table 't2' was not locked with LOCK TABLES
+UNLOCK TABLES;
+UNLOCK TABLES;
+DROP TABLE t1;
 create table t1 (f1 int(12) unsigned not null auto_increment, primary key(f1)) engine=innodb;
 lock tables t1 write;
  alter table t1 auto_increment=0; alter table t1 auto_increment=0; alter table t1 auto_increment=0; alter table t1 auto_increment=0; alter table t1 auto_increment=0; //

mysql-test/t/lock_multi.test

@@ -142,6 +142,7 @@ disconnect con2;
 --error ER_DB_DROP_EXISTS
 DROP DATABASE mysqltest_1;
 
+#
 # Bug#16986 - Deadlock condition with MyISAM tables
 #
 connection locker;
@@ -170,6 +171,55 @@ connection locker;
 use test;
 #
 connection default;
+#
+# Test if CREATE TABLE with LOCK TABLE deadlocks.
+#
+connection writer;
+CREATE TABLE t1 (c1 int);
+LOCK TABLE t1 WRITE;
+#
+# This waits until t1 is unlocked.
+connection locker;
+send FLUSH TABLES WITH READ LOCK;
+--sleep 1
+#
+# This must not block.
+connection writer;
+CREATE TABLE t2 (c1 int);
+UNLOCK TABLES;
+#
+# This awakes now.
+connection locker;
+reap;
+UNLOCK TABLES;
+#
+connection default;
+DROP TABLE t1, t2;
+#
+# Test if CREATE TABLE SELECT with LOCK TABLE deadlocks.
+#
+connection writer;
+CREATE TABLE t1 (c1 int);
+LOCK TABLE t1 WRITE;
+#
+# This waits until t1 is unlocked.
+connection locker;
+send FLUSH TABLES WITH READ LOCK;
+--sleep 1
+#
+# This must not block.
+connection writer;
+--error 1100
+CREATE TABLE t2 AS SELECT * FROM t1;
+UNLOCK TABLES;
+#
+# This awakes now.
+connection locker;
+reap;
+UNLOCK TABLES;
+#
+connection default;
+DROP TABLE t1;
 
 #
 # Bug #17264: MySQL Server freeze

mysys/thr_lock.c

@@ -204,6 +204,8 @@ static void check_locks(THR_LOCK *lock, const char *where,
       {
 	if ((int) data->type == (int) TL_READ_NO_INSERT)
 	  count++;
+        /* Protect against infinite loop. */
+        DBUG_ASSERT(count <= lock->read_no_write_count);
       }
       if (count != lock->read_no_write_count)
       {

sql/lock.cc

@@ -905,7 +905,7 @@ void unlock_table_name(THD *thd, TABLE_LIST *table_list)
   if (table_list->table)
   {
     hash_delete(&open_cache, (byte*) table_list->table);
-    (void) pthread_cond_broadcast(&COND_refresh);
+    broadcast_refresh();
   }
 }
 
@@ -997,9 +997,9 @@ end:
 			(default 0, which will unlock all tables)
 
   NOTES
-    One must have a lock on LOCK_open when calling this
-    This function will send a COND_refresh signal to inform other threads
-    that the name locks are removed
+    One must have a lock on LOCK_open when calling this.
+    This function will broadcast refresh signals to inform other threads
+    that the name locks are removed.
 
   RETURN
     0	ok
@@ -1013,7 +1013,7 @@ void unlock_table_names(THD *thd, TABLE_LIST *table_list,
        table != last_table;
        table= table->next_local)
     unlock_table_name(thd,table);
-  pthread_cond_broadcast(&COND_refresh);
+  broadcast_refresh();
 }
 
 
@@ -1304,3 +1304,37 @@ bool make_global_read_lock_block_commit(THD *thd)
 }
 
 
+/*
+  Broadcast COND_refresh and COND_global_read_lock.
+
+  SYNOPSIS
+    broadcast_refresh()
+      void                      No parameters.
+
+  DESCRIPTION
+    Due to a bug in a threading library it could happen that a signal
+    did not reach its target. A condition for this was that the same
+    condition variable was used with different mutexes in
+    pthread_cond_wait(). Some time ago we changed LOCK_open to
+    LOCK_global_read_lock in global read lock handling. So COND_refresh
+    was used with LOCK_open and LOCK_global_read_lock.
+
+    We did now also change from COND_refresh to COND_global_read_lock
+    in global read lock handling. But now it is necessary to signal
+    both conditions at the same time.
+
+  NOTE
+    When signalling COND_global_read_lock within the global read lock
+    handling, it is not necessary to also signal COND_refresh.
+
+  RETURN
+    void
+*/
+
+void broadcast_refresh(void)
+{
+  VOID(pthread_cond_broadcast(&COND_refresh));
+  VOID(pthread_cond_broadcast(&COND_global_read_lock));
+}
+
+

sql/mysql_priv.h

@@ -1342,6 +1342,7 @@ void start_waiting_global_read_lock(THD *thd);
 bool make_global_read_lock_block_commit(THD *thd);
 bool set_protect_against_global_read_lock(void);
 void unset_protect_against_global_read_lock(void);
+void broadcast_refresh(void);
 
 /* Lock based on name */
 int lock_and_wait_for_table_name(THD *thd, TABLE_LIST *table_list);

sql/sql_base.cc

@@ -530,7 +530,7 @@ void close_thread_tables(THD *thd, bool lock_in_use, bool skip_derived)
   if (found_old_table)
   {
     /* Tell threads waiting for refresh that something has happened */
-    VOID(pthread_cond_broadcast(&COND_refresh));
+    broadcast_refresh();
   }
   if (!lock_in_use)
     VOID(pthread_mutex_unlock(&LOCK_open));
@@ -1035,7 +1035,7 @@ TABLE *unlink_open_table(THD *thd, TABLE *list, TABLE *find)
   }
   *prev=0;
   // Notify any 'refresh' threads
-  pthread_cond_broadcast(&COND_refresh);
+  broadcast_refresh();
   return start;
 }
 
@@ -1577,7 +1577,7 @@ bool reopen_table(TABLE *table,bool locked)
   if (table->triggers)
     table->triggers->set_table(table);
 
-  VOID(pthread_cond_broadcast(&COND_refresh));
+  broadcast_refresh();
   error=0;
 
  end:
@@ -1678,7 +1678,7 @@ bool reopen_tables(THD *thd,bool get_locks,bool in_refresh)
   {
     my_afree((gptr) tables);
   }
-  VOID(pthread_cond_broadcast(&COND_refresh)); // Signal to refresh
+  broadcast_refresh();
   *prev=0;
   DBUG_RETURN(error);
 }
@@ -1715,7 +1715,7 @@ void close_old_data_files(THD *thd, TABLE *table, bool abort_locks,
     }
   }
   if (found)
-    VOID(pthread_cond_broadcast(&COND_refresh)); // Signal to refresh
+    broadcast_refresh();
   DBUG_VOID_RETURN;
 }
 
@@ -1807,7 +1807,7 @@ bool drop_locked_tables(THD *thd,const char *db, const char *table_name)
   }
   *prev=0;
   if (found)
-    VOID(pthread_cond_broadcast(&COND_refresh)); // Signal to refresh
+    broadcast_refresh();
   if (thd->locked_tables && thd->locked_tables->table_count == 0)
   {
     my_free((gptr) thd->locked_tables,MYF(0));
@@ -5249,7 +5249,7 @@ bool remove_table_from_cache(THD *thd, const char *db, const char *table_name,
         Signal any thread waiting for tables to be freed to
         reopen their tables
       */
-      (void) pthread_cond_broadcast(&COND_refresh);
+      broadcast_refresh();
       DBUG_PRINT("info", ("Waiting for refresh signal"));
       if (!(flags & RTFC_CHECK_KILLED_FLAG) || !thd->killed)
       {

sql/sql_handler.cc

@@ -254,7 +254,8 @@ err:
 
   DESCRIPTION
     Though this function takes a list of tables, only the first list entry
-    will be closed. Broadcasts a COND_refresh condition.
+    will be closed.
+    Broadcasts refresh if it closed the table.
 
   RETURN
     FALSE ok
@@ -291,7 +292,7 @@ bool mysql_ha_close(THD *thd, TABLE_LIST *tables)
       if (close_thread_table(thd, table_ptr))
       {
         /* Tell threads waiting for refresh that something has happened */
-        VOID(pthread_cond_broadcast(&COND_refresh));
+        broadcast_refresh();
       }
       VOID(pthread_mutex_unlock(&LOCK_open));
     }
@@ -608,7 +609,7 @@ err0:
     tables are closed (if MYSQL_HA_FLUSH_ALL) is set.
     If 'tables' is NULL and MYSQL_HA_FLUSH_ALL is not set,
     all HANDLER tables marked for flush are closed.
-    Broadcasts a COND_refresh condition, for every table closed.
+    Broadcasts refresh for every table closed.
 
   NOTE
     Since mysql_ha_flush() is called when the base table has to be closed,
@@ -704,7 +705,7 @@ int mysql_ha_flush(THD *thd, TABLE_LIST *tables, uint mode_flags,
                                 MYSQL_HA_REOPEN_ON_USAGE mark for reopen.
 
   DESCRIPTION
-    Broadcasts a COND_refresh condition, for every table closed.
+    Broadcasts refresh if it closed the table.
     The caller must lock LOCK_open.
 
   RETURN
@@ -742,7 +743,7 @@ static int mysql_ha_flush_table(THD *thd, TABLE **table_ptr, uint mode_flags)
   if (close_thread_table(thd, table_ptr))
   {
     /* Tell threads waiting for refresh that something has happened */
-    VOID(pthread_cond_broadcast(&COND_refresh));
+    broadcast_refresh();
   }
 
   DBUG_RETURN(0);

sql/sql_insert.cc

@@ -1349,18 +1349,6 @@ static TABLE *delayed_get_table(THD *thd,TABLE_LIST *table_list)
     */
     if (! (tmp= find_handler(thd, table_list)))
     {
-      /*
-        Avoid that a global read lock steps in while we are creating the
-        new thread. It would block trying to open the table. Hence, the
-        DI thread and this thread would wait until after the global
-        readlock is gone. Since the insert thread needs to wait for a
-        global read lock anyway, we do it right now. Note that
-        wait_if_global_read_lock() sets a protection against a new
-        global read lock when it succeeds. This needs to be released by
-        start_waiting_global_read_lock().
-      */
-      if (wait_if_global_read_lock(thd, 0, 1))
-        goto err;
       if (!(tmp=new delayed_insert()))
       {
 	my_error(ER_OUTOFMEMORY,MYF(0),sizeof(delayed_insert));
@@ -1401,11 +1389,6 @@ static TABLE *delayed_get_table(THD *thd,TABLE_LIST *table_list)
 	pthread_cond_wait(&tmp->cond_client,&tmp->mutex);
       }
       pthread_mutex_unlock(&tmp->mutex);
-      /*
-        Release the protection against the global read lock and wake
-        everyone, who might want to set a global read lock.
-      */
-      start_waiting_global_read_lock(thd);
       thd->proc_info="got old table";
       if (tmp->thd.killed)
       {
@@ -1441,11 +1424,6 @@ static TABLE *delayed_get_table(THD *thd,TABLE_LIST *table_list)
 
  err1:
   thd->fatal_error();
-  /*
-    Release the protection against the global read lock and wake
-    everyone, who might want to set a global read lock.
-  */
-  start_waiting_global_read_lock(thd);
  err:
   pthread_mutex_unlock(&LOCK_delayed_create);
   DBUG_RETURN(0); // Continue with normal insert
@@ -2676,7 +2654,7 @@ bool select_create::send_eof()
       hash_delete(&open_cache,(byte*) table);
       /* Tell threads waiting for refresh that something has happened */
       if (version != refresh_version)
-        VOID(pthread_cond_broadcast(&COND_refresh));
+        broadcast_refresh();
     }
     lock=0;
     table=0;
@@ -2705,7 +2683,7 @@ void select_create::abort()
         quick_rm_table(table_type, create_table->db, create_table->table_name);
       /* Tell threads waiting for refresh that something has happened */
       if (version != refresh_version)
-        VOID(pthread_cond_broadcast(&COND_refresh));
+        broadcast_refresh();
     }
     else if (!create_info->table_existed)
       close_temporary_table(thd, create_table->db, create_table->table_name);

sql/sql_parse.cc

@@ -2337,15 +2337,35 @@ static void reset_one_shot_variables(THD *thd)
 }
 
 
-/****************************************************************************
-** mysql_execute_command
-** Execute command saved in thd and current_lex->sql_command
-****************************************************************************/
+/*
+  Execute command saved in thd and current_lex->sql_command
+
+  SYNOPSIS
+    mysql_execute_command()
+      thd                       Thread handle
+
+  IMPLEMENTATION
+
+    Before every operation that can request a write lock for a table
+    wait if a global read lock exists. However do not wait if this
+    thread has locked tables already. No new locks can be requested
+    until the other locks are released. The thread that requests the
+    global read lock waits for write locked tables to become unlocked.
+
+    Note that wait_if_global_read_lock() sets a protection against a new
+    global read lock when it succeeds. This needs to be released by
+    start_waiting_global_read_lock() after the operation.
+
+  RETURN
+    FALSE       OK
+    TRUE        Error
+*/
 
 bool
 mysql_execute_command(THD *thd)
 {
   bool res= FALSE;
+  bool need_start_waiting= FALSE; // have protection against global read lock
   int  result= 0;
   LEX  *lex= thd->lex;
   /* first SELECT_LEX (have special meaning for many of non-SELECTcommands) */
@@ -2832,7 +2852,8 @@ mysql_execute_command(THD *thd)
       TABLE in the same way. That way we avoid that a new table is
       created during a gobal read lock.
     */
-    if (wait_if_global_read_lock(thd, 0, 1))
+    if (!thd->locked_tables &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
     {
       res= 1;
       goto end_with_restore_list;
@@ -2857,7 +2878,7 @@ mysql_execute_command(THD *thd)
           {
             update_non_unique_table_error(create_table, "CREATE", duplicate);
             res= 1;
-            goto end_with_restart_wait;
+            goto end_with_restore_list;
           }
         }
         /* If we create merge table, we have to test tables in merge, too */
@@ -2873,7 +2894,7 @@ mysql_execute_command(THD *thd)
             {
               update_non_unique_table_error(tab, "CREATE", duplicate);
               res= 1;
-              goto end_with_restart_wait;
+              goto end_with_restore_list;
             }
           }
         }
@@ -2915,13 +2936,6 @@ mysql_execute_command(THD *thd)
 	send_ok(thd);
     }
 
-end_with_restart_wait:
-    /*
-      Release the protection against the global read lock and wake
-      everyone, who might want to set a global read lock.
-    */
-    start_waiting_global_read_lock(thd);
-
     /* put tables back for PS rexecuting */
 end_with_restore_list:
     lex->link_first_table_back(create_table, link_to_local);
@@ -3039,6 +3053,13 @@ end_with_restore_list:
 	goto error;
       else
       {
+        if (!thd->locked_tables &&
+            !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+        {
+          res= 1;
+          break;
+        }
+
         thd->enable_slow_log= opt_log_slow_admin_statements;
 	res= mysql_alter_table(thd, select_lex->db, lex->name,
 			       &lex->create_info,
@@ -3296,6 +3317,14 @@ end_with_restore_list:
       break;
     /* Skip first table, which is the table we are inserting in */
     select_lex->context.table_list= first_table->next_local;
+
+    if (!thd->locked_tables &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+    {
+      res= 1;
+      break;
+    }
+
     res= mysql_insert(thd, all_tables, lex->field_list, lex->many_values,
 		      lex->update_list, lex->value_list,
                       lex->duplicates, lex->ignore);
@@ -3319,6 +3348,14 @@ end_with_restore_list:
     select_lex->options|= SELECT_NO_UNLOCK;
 
     unit->set_limit(select_lex);
+
+    if (! thd->locked_tables &&
+        ! (need_start_waiting= ! wait_if_global_read_lock(thd, 0, 1)))
+    {
+      res= 1;
+      break;
+    }
+
     if (!(res= open_and_lock_tables(thd, all_tables)))
     {
       /* Skip first table, which is the table we are inserting in */
@@ -3395,6 +3432,14 @@ end_with_restore_list:
       break;
     DBUG_ASSERT(select_lex->offset_limit == 0);
     unit->set_limit(select_lex);
+
+    if (!thd->locked_tables &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+    {
+      res= 1;
+      break;
+    }
+
     res = mysql_delete(thd, all_tables, select_lex->where,
                        &select_lex->order_list,
                        unit->select_limit_cnt, select_lex->options,
@@ -3408,6 +3453,13 @@ end_with_restore_list:
       (TABLE_LIST *)thd->lex->auxilliary_table_list.first;
     multi_delete *result;
 
+    if (!thd->locked_tables &&
+        !(need_start_waiting= !wait_if_global_read_lock(thd, 0, 1)))
+    {
+      res= 1;
+      break;
+    }
+
     if ((res= multi_delete_precheck(thd, all_tables)))
       break;
 
@@ -4974,10 +5026,22 @@ end_with_restore_list:
   if (lex->sql_command != SQLCOM_CALL && lex->sql_command != SQLCOM_EXECUTE &&
       uc_update_queries[lex->sql_command]<2)
     thd->row_count_func= -1;
-  DBUG_RETURN(res || thd->net.report_error);
+
+  goto end;
 
 error:
-  DBUG_RETURN(1);
+  res= TRUE;
+
+end:
+  if (need_start_waiting)
+  {
+    /*
+      Release the protection against the global read lock and wake
+      everyone, who might want to set a global read lock.
+    */
+    start_waiting_global_read_lock(thd);
+  }
+  DBUG_RETURN(res || thd->net.report_error);
 }
 
 

sql/sql_table.cc

@@ -1674,8 +1674,6 @@ bool mysql_create_table(THD *thd,const char *db, const char *table_name,
     my_error(ER_TABLE_EXISTS_ERROR, MYF(0), alias);
     DBUG_RETURN(TRUE);
   }
-  if (wait_if_global_read_lock(thd, 0, 1))
-    DBUG_RETURN(TRUE);
   VOID(pthread_mutex_lock(&LOCK_open));
   if (!internal_tmp_table && !(create_info->options & HA_LEX_CREATE_TMP_TABLE))
   {
@@ -1743,7 +1741,6 @@ bool mysql_create_table(THD *thd,const char *db, const char *table_name,
 
 end:
   VOID(pthread_mutex_unlock(&LOCK_open));
-  start_waiting_global_read_lock(thd);
   thd->proc_info="After create";
   DBUG_RETURN(error);
 
@@ -1923,7 +1920,7 @@ void close_cached_table(THD *thd, TABLE *table)
   thd->open_tables=unlink_open_table(thd,thd->open_tables,table);
 
   /* When lock on LOCK_open is freed other threads can continue */
-  pthread_cond_broadcast(&COND_refresh);
+  broadcast_refresh();
   DBUG_VOID_RETURN;
 }
 
@@ -3894,7 +3891,7 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   if (error)
   {
     VOID(pthread_mutex_unlock(&LOCK_open));
-    VOID(pthread_cond_broadcast(&COND_refresh));
+    broadcast_refresh();
     goto err;
   }
   thd->proc_info="end";
@@ -3904,7 +3901,7 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
     Query_log_event qinfo(thd, thd->query, thd->query_length, FALSE, FALSE);
     mysql_bin_log.write(&qinfo);
   }
-  VOID(pthread_cond_broadcast(&COND_refresh));
+  broadcast_refresh();
   VOID(pthread_mutex_unlock(&LOCK_open));
 #ifdef HAVE_BERKELEY_DB
   if (old_db_type == DB_TYPE_BERKELEY_DB)