BUG#24009272 SEGFAULT WITH CREATE+SELECT FROM IS+DROP FTS TABLE CONCURRENTLY

Analysis:
When we access fts_internal_tbl_name in i_s_fts_config_fill (),
it can be set to NULL by another session.

Solution:
Define fts_internal_tbl_name2 for global variable innodb_ft_aux_table,
if it's NULL, set fts_internal_tbl_name to "default".
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
RB: 13401

storage/innobase/fts/fts0fts.cc

@@ -93,6 +93,7 @@ static const ulint FTS_DEADLOCK_RETRY_WAIT = 100000;
 /** variable to record innodb_fts_internal_tbl_name for information
 schema table INNODB_FTS_INSERTED etc. */
 char* fts_internal_tbl_name		= NULL;
+char* fts_internal_tbl_name2		= NULL;
 
 /** InnoDB default stopword list:
 There are different versions of stopwords, the stop words listed

storage/innobase/handler/ha_innodb.cc

@@ -18773,6 +18773,41 @@ innodb_internal_table_validate(
 }
 
 #ifdef BTR_CUR_HASH_ADAPT
+/****************************************************************//**
+Update global variable "fts_internal_tbl_name" with the "saved"
+stopword table name value. This function is registered as a callback
+with MySQL. */
+static
+void
+innodb_internal_table_update(
+/*=========================*/
+	THD*				thd,	/*!< in: thread handle */
+	struct st_mysql_sys_var*	var,	/*!< in: pointer to
+						system variable */
+	void*				var_ptr,/*!< out: where the
+						formal string goes */
+	const void*			save)	/*!< in: immediate result
+						from check function */
+{
+	const char*	table_name;
+	char*		old;
+
+	ut_a(save != NULL);
+	ut_a(var_ptr != NULL);
+
+	table_name = *static_cast<const char*const*>(save);
+	old = *(char**) var_ptr;
+	*(char**) var_ptr = table_name ? my_strdup(table_name, MYF(0)) : NULL;
+	my_free(old);
+
+	fts_internal_tbl_name2 = *(char**) var_ptr;
+	if (fts_internal_tbl_name2 == NULL) {
+		fts_internal_tbl_name = const_cast<char*>("default");
+	} else {
+		fts_internal_tbl_name = fts_internal_tbl_name2;
+	}
+}
+
 /****************************************************************//**
 Update the system variable innodb_adaptive_hash_index using the "saved"
 value. This function is registered as a callback with MySQL. */
@@ -21226,11 +21261,11 @@ static MYSQL_SYSVAR_BOOL(disable_sort_file_cache, srv_disable_sort_file_cache,
   "Whether to disable OS system file cache for sort I/O",
   NULL, NULL, FALSE);
 
-static MYSQL_SYSVAR_STR(ft_aux_table, fts_internal_tbl_name,
-  PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_MEMALLOC,
+static MYSQL_SYSVAR_STR(ft_aux_table, fts_internal_tbl_name2,
+  PLUGIN_VAR_RQCMDARG,
   "FTS internal auxiliary table to be checked",
   innodb_internal_table_validate,
-  NULL, NULL);
+  innodb_internal_table_update, NULL);
 
 static MYSQL_SYSVAR_ULONG(ft_cache_size, fts_max_cache_size,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,

storage/innobase/handler/i_s.cc

@@ -3955,6 +3955,8 @@ i_s_fts_config_fill(
 		DBUG_RETURN(0);
 	}
 
+	DEBUG_SYNC_C("i_s_fts_config_fille_check");
+
 	fields = table->field;
 
 	/* Prevent DDL to drop fts aux tables. */

storage/innobase/include/fts0fts.h

@@ -409,6 +409,7 @@ extern bool		fts_need_sync;
 /** Variable specifying the table that has Fulltext index to display its
 content through information schema table */
 extern char*		fts_internal_tbl_name;
+extern char*		fts_internal_tbl_name2;
 
 #define	fts_que_graph_free(graph)			\
 do {							\