MDEV-13057 innodb_read_only=1 should avoid creating buf_flush_page_cleaner_thread

When the server is started in innodb_read_only mode, there cannot be
any writes to persistent InnoDB/XtraDB files. Just like the creation
of buf_flush_page_cleaner_thread is skipped in this case, also
the creation of the XtraDB-specific buf_flush_lru_manager_thread
should be skipped.

mysql-test/suite/sys_vars/r/innodb_sched_priority_cleaner_basic.result

-SET @start_value = @@GLOBAL.innodb_sched_priority_cleaner;
+SET GLOBAL innodb_sched_priority_cleaner=39;
 SELECT @@GLOBAL.innodb_sched_priority_cleaner;
 @@GLOBAL.innodb_sched_priority_cleaner
 19

mysql-test/suite/sys_vars/t/innodb_sched_priority_cleaner_basic.test

@@ -4,7 +4,15 @@
 
 # A dynamic, global variable
 
-SET @start_value = @@GLOBAL.innodb_sched_priority_cleaner;
+# Test in read-only mode
+--let $restart_parameters= --innodb-read-only
+--source include/restart_mysqld.inc
+--let $restart_parameters=
+
+# This has no actual effect in innodb_read_only mode
+SET GLOBAL innodb_sched_priority_cleaner=39;
+
+--source include/restart_mysqld.inc
 
 # Default value
 SELECT @@GLOBAL.innodb_sched_priority_cleaner;

storage/xtradb/buf/buf0flu.cc

@@ -61,7 +61,7 @@ doing the shutdown */
 UNIV_INTERN bool buf_page_cleaner_is_active;
 
 /** Flag indicating if the lru_manager is in active state. */
-UNIV_INTERN bool buf_lru_manager_is_active = false;
+UNIV_INTERN bool buf_lru_manager_is_active;
 
 #ifdef UNIV_PFS_THREAD
 UNIV_INTERN mysql_pfs_key_t buf_page_cleaner_thread_key;
@@ -2868,8 +2868,6 @@ DECLARE_THREAD(buf_flush_lru_manager_thread)(
 		os_thread_pf(os_thread_get_curr_id()));
 #endif /* UNIV_DEBUG_THREAD_CREATION */
 
-	buf_lru_manager_is_active = true;
-
 	/* On server shutdown, the LRU manager thread runs through cleanup
 	phase to provide free pages for the master and purge threads.  */
 	while (srv_shutdown_state == SRV_SHUTDOWN_NONE

storage/xtradb/handler/ha_innodb.cc

@@ -17032,6 +17032,10 @@ innodb_sched_priority_cleaner_update(
 	const void*			save)	/*!< in: immediate result
 						from check function */
 {
+	if (srv_read_only_mode) {
+		return;
+	}
+
 	ulint	priority = *static_cast<const ulint *>(save);
 	ulint	actual_priority;
 	ulint	nice = 0;
@@ -17058,10 +17062,6 @@ innodb_sched_priority_cleaner_update(
 	}
 
 	/* Set the priority for the page cleaner thread */
-	if (srv_read_only_mode) {
-
-		return;
-	}
 
 	ut_ad(buf_page_cleaner_is_active);
 	nice = os_thread_get_priority(srv_cleaner_tid);

storage/xtradb/srv/srv0start.cc

@@ -2947,12 +2947,15 @@ innobase_start_or_create_for_mysql()
 
 	if (!srv_read_only_mode) {
 		buf_page_cleaner_is_active = true;
-		buf_flush_page_cleaner_thread_handle = os_thread_create(buf_flush_page_cleaner_thread, NULL, NULL);
+		buf_flush_page_cleaner_thread_handle = os_thread_create(
+			buf_flush_page_cleaner_thread, NULL, NULL);
 		buf_flush_page_cleaner_thread_started = true;
-	}
 
-	buf_flush_lru_manager_thread_handle = os_thread_create(buf_flush_lru_manager_thread, NULL, NULL);
-	buf_flush_lru_manager_thread_started = true;
+		buf_lru_manager_is_active = true;
+		buf_flush_lru_manager_thread_handle = os_thread_create(
+			buf_flush_lru_manager_thread, NULL, NULL);
+		buf_flush_lru_manager_thread_started = true;
+	}
 
 	if (!srv_file_per_table && srv_pass_corrupt_table) {
 		fprintf(stderr, "InnoDB: Warning:"