From 5e42d4c123ba9b89ce19b3aa7e22b7684cbfa49c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 9 Oct 2025 16:09:25 +0200 Subject: [PATCH] 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: Dietmar Eggemann Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/deadline.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 933bd1f82c745..fd147a78f7ed2 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -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 -- 2.47.3