Commit 5e42d4c1 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched/deadline: Prepare for switched_from() change 



Prepare for the sched_class::switch*() methods getting folded into the
change pattern. As a result of that, the location of switched_from
will change slightly. SCHED_DEADLINE is affected by this change in
location:

  OLD                              NEW
				|
				|  switching_from()
  dequeue_task();		|  dequeue_task()
  put_prev_task();		|  put_prev_task()
				|  switched_from()
				|
  ... change task ...		|  ... change task ...
				|
  switching_to();		|  switching_to()
  enqueue_task();		|  enqueue_task()
  set_next_task();		|  set_next_task()
  prev_class->switched_from()	|
  switched_to()			|  switched_to()
				|

Notably, where switched_from() was called *after* the change to the
task, it will get called before it. Specifically, switched_from_dl()
uses dl_task(p) which uses p->prio; which is changed when switching
class (it might be the reason to switch class in case of PI).

When switched_from_dl() gets called, the task will have left the
deadline class and dl_task() must be false, while when doing
dequeue_dl_entity() the task must be a dl_task(), otherwise we'd have
called a different dequeue method.

Reported-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
parent 376f8963

kernel/sched/deadline.c

+5 −5
Original line number Diff line number Diff line
@@ -405,7 +405,7 @@ static void __dl_clear_params(struct sched_dl_entity *dl_se); 
 * up, and checks if the task is still in the "ACTIVE non contending"

 * state or not (in the second case, it updates running_bw).

 */

static void task_non_contending(struct sched_dl_entity *dl_se)

static void task_non_contending(struct sched_dl_entity *dl_se, bool dl_task)

{

	struct hrtimer *timer = &dl_se->inactive_timer;

	struct rq *rq = rq_of_dl_se(dl_se);
@@ -444,10 +444,10 @@ static void task_non_contending(struct sched_dl_entity *dl_se) 
		} else {

			struct task_struct *p = dl_task_of(dl_se);



			if (dl_task(p))

			if (dl_task)

				sub_running_bw(dl_se, dl_rq);



			if (!dl_task(p) || READ_ONCE(p->__state) == TASK_DEAD) {

			if (!dl_task || READ_ONCE(p->__state) == TASK_DEAD) {

				struct dl_bw *dl_b = dl_bw_of(task_cpu(p));



				if (READ_ONCE(p->__state) == TASK_DEAD)
@@ -2045,7 +2045,7 @@ static void dequeue_dl_entity(struct sched_dl_entity *dl_se, int flags) 
	 * or "inactive")

	 */

	if (flags & DEQUEUE_SLEEP)

		task_non_contending(dl_se);

		task_non_contending(dl_se, true);

}



static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
@@ -2970,7 +2970,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p) 
	 * will reset the task parameters.

	 */

	if (task_on_rq_queued(p) && p->dl.dl_runtime)

		task_non_contending(&p->dl);

		task_non_contending(&p->dl, false);



	/*

	 * In case a task is setscheduled out from SCHED_DEADLINE we need to