[PATCH 06/24] sched: Allow sched_class::dequeue_task() to fail

Peter Zijlstra
2024-07-27T11:02:28Z

Change the function signature of sched_class::dequeue_task() to return
a boolean, allowing future patches to 'fail' dequeue.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 7 +++++--
kernel/sched/deadline.c | 4 +++-
kernel/sched/fair.c | 4 +++-
kernel/sched/idle.c | 3 ++-
kernel/sched/rt.c | 4 +++-
kernel/sched/sched.h | 4 ++--
kernel/sched/stop_task.c | 3 ++-
7 files changed, 20 insertions(+), 9 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2001,7 +2001,10 @@ void enqueue_task(struct rq *rq, struct
sched_core_enqueue(rq, p);
}

-void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
+/*
+ * Must only return false when DEQUEUE_SLEEP.
+ */
+inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
if (sched_core_enabled(rq))
sched_core_dequeue(rq, p, flags);
@@ -2015,7 +2018,7 @@ void dequeue_task(struct rq *rq, struct
}

uclamp_rq_dec(rq, p);
- p->sched_class->dequeue_task(rq, p, flags);
+ return p->sched_class->dequeue_task(rq, p, flags);
}

void activate_task(struct rq *rq, struct task_struct *p, int flags)
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2162,7 +2162,7 @@ static void enqueue_task_dl(struct rq *r
enqueue_pushable_dl_task(rq, p);
}

-static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
+static bool dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
update_curr_dl(rq);

@@ -2172,6 +2172,8 @@ static void dequeue_task_dl(struct rq *r
dequeue_dl_entity(&p->dl, flags);
if (!p->dl.dl_throttled && !dl_server(&p->dl))
dequeue_pushable_dl_task(rq, p);
+
+ return true;
}

/*
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6865,7 +6865,7 @@ static void set_next_buddy(struct sched_
* decreased. We remove the task from the rbtree and
* update the fair scheduling stats:
*/
-static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
+static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
struct cfs_rq *cfs_rq;
struct sched_entity *se = &p->se;
@@ -6937,6 +6937,8 @@ static void dequeue_task_fair(struct rq
dequeue_throttle:
util_est_update(&rq->cfs, p, task_sleep);
hrtick_update(rq);
+
+ return true;
}

#ifdef CONFIG_SMP
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -482,13 +482,14 @@ struct task_struct *pick_next_task_idle(
* It is not legal to sleep in the idle task - print a warning
* message if some code attempts to do it:
*/
-static void
+static bool
dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
{
raw_spin_rq_unlock_irq(rq);
printk(KERN_ERR "bad: scheduling from the idle thread!\n");
dump_stack();
raw_spin_rq_lock_irq(rq);
+ return true;
}

/*
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1483,7 +1483,7 @@ enqueue_task_rt(struct rq *rq, struct ta
enqueue_pushable_task(rq, p);
}

-static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
+static bool dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
{
struct sched_rt_entity *rt_se = &p->rt;

@@ -1491,6 +1491,8 @@ static void dequeue_task_rt(struct rq *r
dequeue_rt_entity(rt_se, flags);

dequeue_pushable_task(rq, p);
+
+ return true;
}

/*
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2285,7 +2285,7 @@ struct sched_class {
#endif

void (*enqueue_task) (struct rq *rq, struct task_struct *p, int flags);
- void (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);
+ bool (*dequeue_task) (struct rq *rq, struct task_struct *p, int flags);
void (*yield_task) (struct rq *rq);
bool (*yield_to_task)(struct rq *rq, struct task_struct *p);

@@ -3606,7 +3606,7 @@ extern int __sched_setaffinity(struct ta
extern void __setscheduler_prio(struct task_struct *p, int prio);
extern void set_load_weight(struct task_struct *p, bool update_load);
extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags);
-extern void dequeue_task(struct rq *rq, struct task_struct *p, int flags);
+extern bool dequeue_task(struct rq *rq, struct task_struct *p, int flags);

extern void check_class_changed(struct rq *rq, struct task_struct *p,
const struct sched_class *prev_class,
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -57,10 +57,11 @@ enqueue_task_stop(struct rq *rq, struct
add_nr_running(rq, 1);
}

-static void
+static bool
dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
{
sub_nr_running(rq, 1);
+ return true;
}

static void yield_task_stop(struct rq *rq)