MDEV-28079 Shutdown hangs after altering innodb partition fts table

- InnoDB purge waits at resume_FTS() while shutting down.
This happens after altering the FTS innodb partition table.
stop_FTS() has been called for each partition, but it calls
resume_FTS() only once and it leads to hang during shutdown.
This issue was introduced by
commit 1bd681c8(MDEV-25506).

mysql-test/suite/parts/r/partition_alter_innodb.result

@@ -48,3 +48,11 @@ alter table t1 add partition (partition p0 values less than (20));
 ERROR HY000: Duplicate partition name p0
 alter table t1 add partition (partition p1 values less than (20)) /* comment */;
 drop table t1;
+#
+# MDEV-28079 Shutdown hangs after altering innodb partition fts table
+#
+CREATE TABLE t1(f1 INT, f2 CHAR(100))ENGINE=InnoDB PARTITION BY HASH(f1) PARTITIONS 2;
+ALTER TABLE t1 ADD FULLTEXT(f2);
+InnoDB		0 transactions not purged
+DROP TABLE t1;
+# End of 10.6 tests

mysql-test/suite/parts/t/partition_alter_innodb.test

@@ -9,3 +9,11 @@ SET GLOBAL innodb_read_only_compressed=OFF;
 --disable_query_log
 SET GLOBAL innodb_read_only_compressed=@save_innodb_read_only_compressed;
 --enable_query_log
+--echo #
+--echo # MDEV-28079 Shutdown hangs after altering innodb partition fts table
+--echo #
+CREATE TABLE t1(f1 INT, f2 CHAR(100))ENGINE=InnoDB PARTITION BY HASH(f1) PARTITIONS 2;
+ALTER TABLE t1 ADD FULLTEXT(f2);
+--source ../innodb/include/wait_all_purged.inc
+DROP TABLE t1;
+--echo # End of 10.6 tests

storage/innobase/fts/fts0fts.cc

@@ -1567,9 +1567,12 @@ static void fts_table_no_ref_count(const char *table_name)
 
 /** Stop the purge thread and check n_ref_count of all auxiliary
 and common table associated with the fts table.
-@param	table	parent FTS table */
-void purge_sys_t::stop_FTS(const dict_table_t &table)
+@param	table		parent FTS table
+@param	already_stopped	True indicates purge threads were
+			already stopped*/
+void purge_sys_t::stop_FTS(const dict_table_t &table, bool already_stopped)
 {
+  if (!already_stopped)
     purge_sys.stop_FTS();
   fts_table_t fts_table;
   char table_name[MAX_FULL_NAME_LEN];

storage/innobase/handler/handler0alter.cc

@@ -10903,12 +10903,14 @@ ha_innobase::commit_inplace_alter_table(
 		}
 	}
 
+	bool already_stopped= false;
 	for (inplace_alter_handler_ctx** pctx = ctx_array; *pctx; pctx++) {
 		auto ctx = static_cast<ha_innobase_inplace_ctx*>(*pctx);
 		dberr_t error = DB_SUCCESS;
 
 		if (fts_exist) {
-			purge_sys.stop_FTS(*ctx->old_table);
+			purge_sys.stop_FTS(*ctx->old_table, already_stopped);
+			already_stopped = true;
 		}
 
 		if (new_clustered && ctx->old_table->fts) {

storage/innobase/include/trx0purge.h

@@ -286,8 +286,10 @@ class purge_sys_t
 
   /** Stop the purge thread and check n_ref_count of all auxiliary
   and common table associated with the fts table.
-  @param table	parent FTS table */
-  void stop_FTS(const dict_table_t &table);
+  @param	table		parent FTS table
+  @param	already_stopped	True indicates purge threads were
+				already stopped */
+  void stop_FTS(const dict_table_t &table, bool already_stopped=false);
 };
 
 /** The global data structure coordinating a purge */