MDEV-33098: Fix some instrumentation for innodb.doublewrite_debug

buf_flush_page_cleaner(): A continue or break inside DBUG_EXECUTE_IF
actually is a no-op. Use an explicit call to _db_keyword_() to
actually avoid advancing the checkpoint.

buf_flush_list_now_set(): Invoke os_aio_wait_until_no_pending_writes()
to ensure that the page write to the system tablespace is completed.

mysql-test/suite/innodb/t/doublewrite_debug.test

@@ -61,17 +61,6 @@ set global innodb_fil_make_page_dirty_debug = 0;
 set global innodb_buf_flush_list_now = 1;
 
 --let CLEANUP_IF_CHECKPOINT=drop table t1, unexpected_checkpoint;
-# Occasionally, a checkpoint would occur on the MSAN builder.
-# We do not know the reason, because the failure can only be reproduced if there is
-# enough load in that environment.
-# Therefore, we allow the test to be skipped when run on MSAN.
-# In other environments, we want the test to fail if a checkpoint occurs,
-# so that we would catch it if it starts to happen regularly.
-if (`select count(*) from information_schema.system_variables where variable_name='have_sanitizer' and global_value like "MSAN%"`)
-{
---let CLEANUP_IF_CHECKPOINT=drop table t1;
-}
-
 --source ../include/no_checkpoint_end.inc
 
 --echo # Make the 1st page (page_no=0) and 2nd page (page_no=1)

storage/innobase/buf/buf0flu.cc

@@ -2333,9 +2333,9 @@ static os_thread_ret_t DECLARE_THREAD(buf_flush_page_cleaner)(void*)
 
       do
       {
-        DBUG_EXECUTE_IF("ib_log_checkpoint_avoid", continue;);
-        DBUG_EXECUTE_IF("ib_log_checkpoint_avoid_hard", continue;);
-
+        IF_DBUG(if (_db_keyword_(nullptr, "ib_log_checkpoint_avoid", 1) ||
+                    _db_keyword_(nullptr, "ib_log_checkpoint_avoid_hard", 1))
+                  continue,);
         if (!recv_recovery_is_on() &&
             !srv_startup_is_before_trx_rollback_phase &&
             srv_operation <= SRV_OPERATION_EXPORT_RESTORED)

storage/innobase/handler/ha_innodb.cc

@@ -18313,7 +18313,10 @@ buf_flush_list_now_set(THD*, st_mysql_sys_var*, void*, const void* save)
   if (s)
     buf_flush_sync();
   else
+  {
     while (buf_flush_list_space(fil_system.sys_space, nullptr));
+    os_aio_wait_until_no_pending_writes();
+  }
   mysql_mutex_lock(&LOCK_global_system_variables);
 }