A fix and a test case for Bug#24918 drop table and lock / inconsistent

between perm and temp tables. Review fixes.

The original bug report complains that if we locked a temporary table
with LOCK TABLES statement, we would not leave LOCK TABLES mode
when this temporary table is dropped.

Additionally, the bug was escalated when it was discovered than
when a temporary transactional table that was previously
locked with LOCK TABLES statement was dropped, futher actions with
this table, such as UNLOCK TABLES, would lead to a crash.

The problem originates from incomplete support of transactional temporary
tables. When we added calls to handler::store_lock()/handler::external_lock()
to operations that work with such tables, we only covered the normal
server code flow and did not cover LOCK TABLES mode. 
In LOCK TABLES mode, ::external_lock(LOCK) would sometimes be called without
matching ::external_lock(UNLOCK), e.g. when a transactional temporary table
was dropped. Additionally, this table would be left in the list of LOCKed 
TABLES.

The patch aims to address this inadequacy. Now, whenever an instance
of 'handler' is destroyed, we assert that it was priorly
external_lock(UNLOCK)-ed. All the places that violate this assert
were fixed.

This patch introduces no changes in behavior -- the discrepancy in
behavior will be fixed when we start calling ::store_lock()/::external_lock()
for all tables, regardless whether they are transactional or not, 
temporary or not.

mysql-test/r/innodb_mysql.result

@@ -739,4 +739,32 @@ drop table if exists t1;
 create table t1 (a int) engine=innodb;
 alter table t1 alter a set default 1;
 drop table t1;
+
+Bug#24918 drop table and lock / inconsistent between 
+perm and temp tables
+
+Check transactional tables under LOCK TABLES
+
+drop table if exists t24918, t24918_tmp, t24918_trans, t24918_trans_tmp, 
+t24918_access;
+create table t24918_access (id int);
+create table t24918 (id int) engine=myisam;
+create temporary table t24918_tmp (id int) engine=myisam;
+create table t24918_trans (id int) engine=innodb;
+create temporary table t24918_trans_tmp (id int) engine=innodb;
+lock table t24918 write, t24918_tmp write, t24918_trans write, t24918_trans_tmp write;
+drop table t24918;
+select * from t24918_access;
+ERROR HY000: Table 't24918_access' was not locked with LOCK TABLES
+drop table t24918_trans;
+select * from t24918_access;
+ERROR HY000: Table 't24918_access' was not locked with LOCK TABLES
+drop table t24918_trans_tmp;
+select * from t24918_access;
+ERROR HY000: Table 't24918_access' was not locked with LOCK TABLES
+drop table t24918_tmp;
+select * from t24918_access;
+ERROR HY000: Table 't24918_access' was not locked with LOCK TABLES
+unlock tables;
+drop table t24918_access;
 End of 5.0 tests

mysql-test/t/innodb_mysql.test

@@ -754,4 +754,38 @@ create table t1 (a int) engine=innodb;
 alter table t1 alter a set default 1;
 drop table t1;
 
+
+--echo
+--echo Bug#24918 drop table and lock / inconsistent between 
+--echo perm and temp tables
+--echo
+--echo Check transactional tables under LOCK TABLES
+--echo
+--disable_warnings
+drop table if exists t24918, t24918_tmp, t24918_trans, t24918_trans_tmp, 
+t24918_access;
+--enable_warnings
+create table t24918_access (id int);
+create table t24918 (id int) engine=myisam;
+create temporary table t24918_tmp (id int) engine=myisam;
+create table t24918_trans (id int) engine=innodb;
+create temporary table t24918_trans_tmp (id int) engine=innodb;
+
+lock table t24918 write, t24918_tmp write, t24918_trans write, t24918_trans_tmp write;
+drop table t24918;
+--error ER_TABLE_NOT_LOCKED
+select * from t24918_access;
+drop table t24918_trans;
+--error ER_TABLE_NOT_LOCKED
+select * from t24918_access;
+drop table t24918_trans_tmp;
+--error ER_TABLE_NOT_LOCKED
+select * from t24918_access;
+drop table t24918_tmp;
+--error ER_TABLE_NOT_LOCKED
+select * from t24918_access;
+unlock tables;
+
+drop table t24918_access;
+
 --echo End of 5.0 tests

sql/handler.h

@@ -508,6 +508,29 @@ class handler :public Sql_alloc
   */
   virtual int rnd_init(bool scan) =0;
   virtual int rnd_end() { return 0; }
+  /**
+    Is not invoked for non-transactional temporary tables.
+
+    Tells the storage engine that we intend to read or write data
+    from the table. This call is prefixed with a call to handler::store_lock()
+    and is invoked only for those handler instances that stored the lock.
+
+    Calls to rnd_init/index_init are prefixed with this call. When table
+    IO is complete, we call external_lock(F_UNLCK).
+    A storage engine writer should expect that each call to
+    ::external_lock(F_[RD|WR]LOCK is followed by a call to
+    ::external_lock(F_UNLCK). If it is not, it is a bug in MySQL.
+
+    The name and signature originate from the first implementation
+    in MyISAM, which would call fcntl to set/clear an advisory
+    lock on the data file in this method.
+
+    @param   lock_type    F_RDLCK, F_WRLCK, F_UNLCK
+
+    @return  non-0 in case of failure, 0 in case of success.
+    When lock_type is F_UNLCK, the return value is ignored.
+  */
+  virtual int external_lock(THD *thd, int lock_type) { return 0; }
 
 public:
   const handlerton *ht;                 /* storage engine of this handler */
@@ -548,6 +571,7 @@ class handler :public Sql_alloc
   uint raid_type,raid_chunks;
   FT_INFO *ft_handler;
   enum {NONE=0, INDEX, RND} inited;
+  bool locked;
   bool  auto_increment_column_changed;
   bool implicit_emptied;                /* Can be !=0 only if HEAP */
   const COND *pushed_cond;
@@ -560,10 +584,11 @@ class handler :public Sql_alloc
     create_time(0), check_time(0), update_time(0),
     key_used_on_scan(MAX_KEY), active_index(MAX_KEY),
     ref_length(sizeof(my_off_t)), block_size(0),
-    raid_type(0), ft_handler(0), inited(NONE), implicit_emptied(0),
+    raid_type(0), ft_handler(0), inited(NONE),
+    locked(FALSE), implicit_emptied(0),
     pushed_cond(NULL)
     {}
-  virtual ~handler(void) { /* TODO: DBUG_ASSERT(inited == NONE); */ }
+  virtual ~handler(void) { DBUG_ASSERT(locked == FALSE); /* TODO: DBUG_ASSERT(inited == NONE); */ }
   virtual handler *clone(MEM_ROOT *mem_root);
   int ha_open(const char *name, int mode, int test_if_locked);
   void adjust_next_insert_id_after_explicit_value(ulonglong nr);
@@ -597,6 +622,13 @@ class handler :public Sql_alloc
 
   virtual const char *index_type(uint key_number) { DBUG_ASSERT(0); return "";}
 
+  int ha_external_lock(THD *thd, int lock_type)
+  {
+    int rc;
+    DBUG_ENTER("ha_external_lock");
+    locked= lock_type != F_UNLCK;
+    DBUG_RETURN(external_lock(thd, lock_type));
+  }
   int ha_index_init(uint idx)
   {
     DBUG_ENTER("ha_index_init");
@@ -689,7 +721,6 @@ class handler :public Sql_alloc
   virtual int extra_opt(enum ha_extra_function operation, ulong cache_size)
   { return extra(operation); }
   virtual int reset() { return extra(HA_EXTRA_RESET); }
-  virtual int external_lock(THD *thd, int lock_type) { return 0; }
   virtual void unlock_row() {}
   virtual int start_stmt(THD *thd, thr_lock_type lock_type) {return 0;}
   /*
@@ -837,6 +868,9 @@ class handler :public Sql_alloc
 
   /* lock_count() can be more than one if the table is a MERGE */
   virtual uint lock_count(void) const { return 1; }
+  /**
+    Is not invoked for non-transactional temporary tables.
+  */
   virtual THR_LOCK_DATA **store_lock(THD *thd,
 				     THR_LOCK_DATA **to,
 				     enum thr_lock_type lock_type)=0;

sql/lock.cc

@@ -151,7 +151,8 @@ MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **tables, uint count,
     }
 
     thd->proc_info="System lock";
-    if (lock_external(thd, tables, count))
+    if (sql_lock->table_count && lock_external(thd, sql_lock->table,
+                                               sql_lock->table_count))
     {
       /* Clear the lock type of all lock data to avoid reusage. */
       reset_lock_data(sql_lock);
@@ -246,12 +247,12 @@ static int lock_external(THD *thd, TABLE **tables, uint count)
 	 (*tables)->reginfo.lock_type <= TL_READ_NO_INSERT))
       lock_type=F_RDLCK;
 
-    if ((error=(*tables)->file->external_lock(thd,lock_type)))
+    if ((error= (*tables)->file->ha_external_lock(thd,lock_type)))
     {
       print_lock_error(error, (*tables)->file->table_type());
       for (; i-- ; tables--)
       {
-	(*tables)->file->external_lock(thd, F_UNLCK);
+	(*tables)->file->ha_external_lock(thd, F_UNLCK);
 	(*tables)->current_lock=F_UNLCK;
       }
       DBUG_RETURN(error);
@@ -353,10 +354,28 @@ void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock)
 }
 
 
+/**
+  Try to find the table in the list of locked tables.
+  In case of success, unlock the table and remove it from this list.
 
-void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table)
+  @note This function has a legacy side effect: the table is
+  unlocked even if it is not found in the locked list.
+  It's not clear if this side effect is intentional or still
+  desirable. It might lead to unmatched calls to
+  unlock_external(). Moreover, a discrepancy can be left
+  unnoticed by the storage engine, because in
+  unlock_external() we call handler::external_lock(F_UNLCK) only
+  if table->current_lock is not F_UNLCK.
+
+  @param  always_unlock   specify explicitly if the legacy side
+                          effect is desired.
+*/
+
+void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table,
+                       bool always_unlock)
 {
-  mysql_unlock_some_tables(thd, &table,1);
+  if (always_unlock == TRUE)
+    mysql_unlock_some_tables(thd, &table, /* table count */ 1);
   if (locked)
   {
     reg1 uint i;
@@ -370,6 +389,10 @@ void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table)
 
         DBUG_ASSERT(table->lock_position == i);
 
+        /* Unlock if not yet unlocked */
+        if (always_unlock == FALSE)
+          mysql_unlock_some_tables(thd, &table, /* table count */ 1);
+
         /* Decrement table_count in advance, making below expressions easier */
         old_tables= --locked->table_count;
 
@@ -623,7 +646,7 @@ static int unlock_external(THD *thd, TABLE **table,uint count)
     if ((*table)->current_lock != F_UNLCK)
     {
       (*table)->current_lock = F_UNLCK;
-      if ((error=(*table)->file->external_lock(thd, F_UNLCK)))
+      if ((error= (*table)->file->ha_external_lock(thd, F_UNLCK)))
       {
 	error_code=error;
 	print_lock_error(error_code, (*table)->file->table_type());

sql/mysql_priv.h

@@ -1452,7 +1452,8 @@ MYSQL_LOCK *mysql_lock_tables(THD *thd, TABLE **table, uint count,
 void mysql_unlock_tables(THD *thd, MYSQL_LOCK *sql_lock);
 void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock);
 void mysql_unlock_some_tables(THD *thd, TABLE **table,uint count);
-void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table);
+void mysql_lock_remove(THD *thd, MYSQL_LOCK *locked,TABLE *table,
+                       bool always_unlock);
 void mysql_lock_abort(THD *thd, TABLE *table);
 bool mysql_lock_abort_for_thread(THD *thd, TABLE *table);
 MYSQL_LOCK *mysql_lock_merge(MYSQL_LOCK *a,MYSQL_LOCK *b);

sql/opt_range.cc

@@ -972,7 +972,7 @@ QUICK_RANGE_SELECT::~QUICK_RANGE_SELECT()
         DBUG_PRINT("info", ("Freeing separate handler 0x%lx (free: %d)", (long) file,
                             free_file));
         file->reset();
-        file->external_lock(current_thd, F_UNLCK);
+        file->ha_external_lock(current_thd, F_UNLCK);
         file->close();
       }
     }
@@ -1142,7 +1142,7 @@ int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler)
     /* Caller will free the memory */
     goto failure;  /* purecov: inspected */
   }
-  if (file->external_lock(thd, F_RDLCK))
+  if (file->ha_external_lock(thd, F_RDLCK))
     goto failure;
   if (!head->no_keyread)
   {
@@ -1152,7 +1152,7 @@ int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler)
   if (file->extra(HA_EXTRA_RETRIEVE_PRIMARY_KEY) ||
       init() || reset())
   {
-    file->external_lock(thd, F_UNLCK);
+    file->ha_external_lock(thd, F_UNLCK);
     file->close();
     goto failure;
   }

sql/sql_base.cc

@@ -1037,6 +1037,31 @@ TABLE **find_temporary_table(THD *thd, const char *db, const char *table_name)
   return 0;					// Not a temporary table
 }
 
+
+/**
+  Drop a temporary table.
+
+  Try to locate the table in the list of thd->temporary_tables.
+  If the table is found:
+   - if the table is in thd->locked_tables, unlock it and
+     remove it from the list of locked tables. Currently only transactional
+     temporary tables are present in the locked_tables list.
+   - Close the temporary table, remove its .FRM
+   - remove the table from the list of temporary tables
+
+  This function is used to drop user temporary tables, as well as
+  internal tables created in CREATE TEMPORARY TABLE ... SELECT
+  or ALTER TABLE. Even though part of the work done by this function
+  is redundant when the table is internal, as long as we
+  link both internal and user temporary tables into the same
+  thd->temporary_tables list, it's impossible to tell here whether
+  we're dealing with an internal or a user temporary table.
+
+  @retval TRUE   the table was not found in the list of temporary tables
+                 of this thread
+  @retval FALSE  the table was found and dropped successfully.
+*/
+
 bool close_temporary_table(THD *thd, const char *db, const char *table_name)
 {
   TABLE *table,**prev;
@@ -1045,6 +1070,11 @@ bool close_temporary_table(THD *thd, const char *db, const char *table_name)
     return 1;
   table= *prev;
   *prev= table->next;
+  /*
+    If LOCK TABLES list is not empty and contains this table,
+    unlock the table and remove the table from this list.
+  */
+  mysql_lock_remove(thd, thd->locked_tables, table, FALSE);
   close_temporary(table, 1);
   if (thd->slave_thread)
     --slave_open_temp_tables;
@@ -1120,7 +1150,7 @@ TABLE *unlink_open_table(THD *thd, TABLE *list, TABLE *find)
 	!memcmp(list->s->table_cache_key, key, key_length))
     {
       if (thd->locked_tables)
-	mysql_lock_remove(thd, thd->locked_tables,list);
+        mysql_lock_remove(thd, thd->locked_tables, list, TRUE);
       VOID(hash_delete(&open_cache,(byte*) list)); // Close table
     }
     else
@@ -1151,6 +1181,8 @@ TABLE *unlink_open_table(THD *thd, TABLE *list, TABLE *find)
           dropped is already unlocked. In the former case it will
           also remove lock on the table. But one should not rely on
           this behaviour as it may change in future.
+          Currently, however, this function is never called for a
+          table that was locked with LOCK TABLES.
 */
 
 void drop_open_table(THD *thd, TABLE *table, const char *db_name,
@@ -2099,7 +2131,7 @@ bool close_data_tables(THD *thd,const char *db, const char *table_name)
     if (!strcmp(table->s->table_name, table_name) &&
 	!strcmp(table->s->db, db))
     {
-      mysql_lock_remove(thd, thd->locked_tables,table);
+      mysql_lock_remove(thd, thd->locked_tables, table, TRUE);
       table->file->close();
       table->db_stat=0;
     }
@@ -2239,7 +2271,7 @@ void close_old_data_files(THD *thd, TABLE *table, bool morph_locks,
             instances of this table.
           */
           mysql_lock_abort(thd, table);
-          mysql_lock_remove(thd, thd->locked_tables, table);
+          mysql_lock_remove(thd, thd->locked_tables, table, TRUE);
           /*
             We want to protect the table from concurrent DDL operations
             (like RENAME TABLE) until we will re-open and re-lock it.
@@ -2343,7 +2375,7 @@ bool drop_locked_tables(THD *thd,const char *db, const char *table_name)
     if (!strcmp(table->s->table_name, table_name) &&
 	!strcmp(table->s->db, db))
     {
-      mysql_lock_remove(thd, thd->locked_tables,table);
+      mysql_lock_remove(thd, thd->locked_tables, table, TRUE);
       VOID(hash_delete(&open_cache,(byte*) table));
       found=1;
     }

sql/sql_class.h

@@ -995,13 +995,25 @@ enum prelocked_mode_type {NON_PRELOCKED= 0, PRELOCKED= 1,
 class Open_tables_state
 {
 public:
-  /*
-    open_tables - list of regular tables in use by this thread
-    temporary_tables - list of temp tables in use by this thread
-    handler_tables - list of tables that were opened with HANDLER OPEN
-     and are still in use by this thread
+  /**
+    List of regular tables in use by this thread. Contains temporary and
+    base tables that were opened with @see open_tables().
+  */
+  TABLE *open_tables;
+  /**
+    List of temporary tables used by this thread. Contains user-level
+    temporary tables, created with CREATE TEMPORARY TABLE, and
+    internal temporary tables, created, e.g., to resolve a SELECT,
+    or for an intermediate table used in ALTER.
+    XXX Why are internal temporary tables added to this list?
+  */
+  TABLE *temporary_tables;
+  /**
+    List of tables that were opened with HANDLER OPEN and are
+    still in use by this thread.
   */
-  TABLE *open_tables, *temporary_tables, *handler_tables, *derived_tables;
+  TABLE *handler_tables;
+  TABLE *derived_tables;
   /*
     During a MySQL session, one can lock tables in two modes: automatic
     or manual. In automatic mode all necessary tables are locked just before

sql/sql_table.cc

@@ -3791,10 +3791,10 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   {
     VOID(pthread_mutex_lock(&LOCK_open));
     wait_while_table_is_used(thd, table, HA_EXTRA_FORCE_REOPEN);
-    table->file->external_lock(thd, F_WRLCK);
+    table->file->ha_external_lock(thd, F_WRLCK);
     alter_table_manage_keys(table, table->file->indexes_are_disabled(),
                             alter_info->keys_onoff);
-    table->file->external_lock(thd, F_UNLCK);
+    table->file->ha_external_lock(thd, F_UNLCK);
     VOID(pthread_mutex_unlock(&LOCK_open));
     error= ha_commit_stmt(thd);
     if (ha_commit(thd))
@@ -3813,7 +3813,7 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
 	The following function call will free the new_table pointer,
 	in close_temporary_table(), so we can safely directly jump to err
       */
-      close_temporary_table(thd,new_db,tmp_name);
+      close_temporary_table(thd, new_db, tmp_name);
       goto err;
     }
     /* Close lock if this is a transactional table */
@@ -4086,7 +4086,7 @@ copy_data_between_tables(TABLE *from,TABLE *to,
   if (!(copy= new Copy_field[to->s->fields]))
     DBUG_RETURN(-1);				/* purecov: inspected */
 
-  if (to->file->external_lock(thd, F_WRLCK))
+  if (to->file->ha_external_lock(thd, F_WRLCK))
     DBUG_RETURN(-1);
 
   /* We need external lock before we can disable/enable keys */
@@ -4238,7 +4238,7 @@ copy_data_between_tables(TABLE *from,TABLE *to,
   free_io_cache(from);
   *copied= found_count;
   *deleted=delete_count;
-  if (to->file->external_lock(thd,F_UNLCK))
+  if (to->file->ha_external_lock(thd,F_UNLCK))
     error=1;
   DBUG_RETURN(error > 0 ? -1 : 0);
 }