MDEV-7083: sys_vars.innodb_sched_priority* tests fail in buildbot

on work-amd64-valgrind.

Fixed issue by finding out first the current used priority
for both treads and using that seeing did we really change
the priority or not.

storage/xtradb/handler/ha_innodb.cc

@@ -16434,19 +16434,24 @@ innodb_sched_priority_cleaner_update(
 {
 	ulint	priority = *static_cast<const ulint *>(save);
 	ulint	actual_priority;
+	ulint	nice = 0;
 
 	/* Set the priority for the LRU manager thread */
 	ut_ad(buf_lru_manager_is_active);
+	nice = os_thread_get_priority(srv_lru_manager_tid);
 	actual_priority = os_thread_set_priority(srv_lru_manager_tid,
 						 priority);
+
 	if (UNIV_UNLIKELY(actual_priority != priority)) {
 
+		if (actual_priority+nice != priority) {
 			push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
 				ER_WRONG_ARGUMENTS,
 				"Failed to set the LRU manager thread "
 				"priority to %lu,  "
-				    "the current priority is %lu", priority,
-				    actual_priority);
+				"the nice is %lu and used priority is %lu", priority,
+				nice, actual_priority);
+		}
 	} else {
 
 		srv_sched_priority_cleaner = priority;
@@ -16459,15 +16464,17 @@ innodb_sched_priority_cleaner_update(
 	}
 
 	ut_ad(buf_page_cleaner_is_active);
+	nice = os_thread_get_priority(srv_cleaner_tid);
 	actual_priority = os_thread_set_priority(srv_cleaner_tid, priority);
 	if (UNIV_UNLIKELY(actual_priority != priority)) {
-
+		if (actual_priority+nice != priority) {
 			push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
 				ER_WRONG_ARGUMENTS,
 				"Failed to set the page cleaner thread "
 				"priority to %lu,  "
-				    "the current priority is %lu", priority,
-				    actual_priority);
+				"the nice is %lu and used priority is %lu", priority,
+				nice, actual_priority);
+		}
 	}
 }
 

storage/xtradb/include/os0thread.h

@@ -182,6 +182,17 @@ os_thread_set_priority(
 	ulint		relative_priority);	/*!< in: system-specific
 						priority value */
 
+/*****************************************************************//**
+Get priority for a given thread on Linux.  Currently a
+no-op on other systems.
+
+@return An actual thread priority */
+UNIV_INTERN
+ulint
+os_thread_get_priority(
+/*===================*/
+	os_tid_t	thread_id);		/*!< in: thread id */
+
 #ifndef UNIV_NONINL
 #include "os0thread.ic"
 #endif

storage/xtradb/os/os0thread.cc

@@ -312,3 +312,21 @@ os_thread_set_priority(
 	return(relative_priority);
 #endif
 }
+
+/*****************************************************************//**
+Get priority for a given thread on Linux.  Currently a
+no-op on other systems.
+
+@return An actual thread priority */
+UNIV_INTERN
+ulint
+os_thread_get_priority(
+/*===================*/
+	os_tid_t	thread_id)		/*!< in: thread id */
+{
+#ifdef UNIV_LINUX
+	return (getpriority(PRIO_PROCESS, thread_id));
+#else
+	return (0);
+#endif
+}