Fix Bug# 58459 - assert slot->in_use == FALSE while starting purge thread.

Fix a race condition in srv_master_thread(). We need to acquire the kernel
mutex before calling srv_table_reserve_slot(). Add a mutex_own() assertion
in srv_table_reserve_slot().

storage/innobase/srv/srv0srv.c

@@ -831,6 +831,7 @@ srv_table_reserve_slot(
 
 	ut_a(type > 0);
 	ut_a(type <= SRV_MASTER);
+	ut_ad(mutex_own(&kernel_mutex));
 
 	i = 0;
 	slot = srv_table_get_nth_slot(i);
@@ -2627,10 +2628,10 @@ srv_master_thread(
 	srv_main_thread_process_no = os_proc_get_number();
 	srv_main_thread_id = os_thread_pf(os_thread_get_curr_id());
 
-	srv_table_reserve_slot(SRV_MASTER);
-
 	mutex_enter(&kernel_mutex);
 
+	srv_table_reserve_slot(SRV_MASTER);
+
 	srv_n_threads_active[SRV_MASTER]++;
 
 	mutex_exit(&kernel_mutex);