determine_next_mode(): check if process is runnable

kernel/sched/sched.h

@@ -904,8 +904,30 @@ static inline int determine_next_mode_pb(struct rq *rq)
 				 * Is the tick interrupt active in this moment?
 				 */
 				if(pb->count_admin_cycles > pb->n_admin_cycles){
+					/*
+					 * If the current plan_entry's process is blocked, we cannot
+					 * go in PB_EXEC_MODE. The reason could be, that administrative
+					 * tasks were pushed forward by the default scheduler and the IO
+					 * starved. We have to wait until the process is runnable.
+					 */
+					if (pb->plan[pb->c_entry].task_struct->state >= 0) {
+						/*
+						 * 0 	== Runnable (IO succeeded)
+						 * >0 	== stopped (Process finished)
+						 */
 						mode = PB_EXEC_MODE;
 						pb->count_admin_cycles = 0;
+
+					} else {
+						/*
+						 * -1	== unrunnable
+						 */
+						mode = PB_ADMIN_MODE;
+						printk(KERN_WARNING "PB TASK %llu BLOCKED BY IO FOR %llu TOO MANY TICKS\n",
+								pb->plan[pb->c_entry].task_id,
+								pb->count_admin_cycles - pb->n_admin_cycles);
+					}
+
 				}else{
 					mode = PB_ADMIN_MODE;
 				}