- Add PREEMPT_RT maintainers

- Fix another aspect of delayed dequeued tasks wrt determining their state,
   i.e., whether they're runnable or blocked
 
 - Handle delayed dequeued tasks and their migration wrt PSI properly
 
 - Fix the situation where a delayed dequeue task gets enqueued into a new
   class, which should not happen
 
 - Fix a case where memory allocation would happen while the runqueue lock is
   held, which is a no-no
 
 - Do not over-schedule when tasks with shorter slices preempt the currently
   running task
 
 - Make sure delayed to deque entities are properly handled before unthrottling
 
 - Other smaller cleanups and improvements
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Merge tag 'sched_urgent_for_v6.12_rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduling fixes from Borislav Petkov:

 - Add PREEMPT_RT maintainers

 - Fix another aspect of delayed dequeued tasks wrt determining their
   state, i.e., whether they're runnable or blocked

 - Handle delayed dequeued tasks and their migration wrt PSI properly

 - Fix the situation where a delayed dequeue task gets enqueued into a
   new class, which should not happen

 - Fix a case where memory allocation would happen while the runqueue
   lock is held, which is a no-no

 - Do not over-schedule when tasks with shorter slices preempt the
   currently running task

 - Make sure delayed to deque entities are properly handled before
   unthrottling

 - Other smaller cleanups and improvements

* tag 'sched_urgent_for_v6.12_rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  MAINTAINERS: Add an entry for PREEMPT_RT.
  sched/fair: Fix external p->on_rq users
  sched/psi: Fix mistaken CPU pressure indication after corrupted task state bug
  sched/core: Dequeue PSI signals for blocked tasks that are delayed
  sched: Fix delayed_dequeue vs switched_from_fair()
  sched/core: Disable page allocation in task_tick_mm_cid()
  sched/deadline: Use hrtick_enabled_dl() before start_hrtick_dl()
  sched/eevdf: Fix wakeup-preempt by checking cfs_rq->nr_running
  sched: Fix sched_delayed vs cfs_bandwidth

MAINTAINERS

@@ -19527,6 +19527,14 @@ S:	Maintained
 F:	Documentation/tools/rtla/
 F:	tools/tracing/rtla/
 
+Real-time Linux (PREEMPT_RT)
+M:	Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+M:	Clark Williams <clrkwllms@kernel.org>
+M:	Steven Rostedt <rostedt@goodmis.org>
+L:	linux-rt-devel@lists.linux.dev
+S:	Supported
+K:	PREEMPT_RT
+
 REALTEK AUDIO CODECS
 M:	Oder Chiou <oder_chiou@realtek.com>
 S:	Maintained

include/linux/sched.h

@@ -2133,6 +2133,11 @@ static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
 
 #endif /* CONFIG_SMP */
 
+static inline bool task_is_runnable(struct task_struct *p)
+{
+	return p->on_rq && !p->se.sched_delayed;
+}
+
 extern bool sched_task_on_rq(struct task_struct *p);
 extern unsigned long get_wchan(struct task_struct *p);
 extern struct task_struct *cpu_curr_snapshot(int cpu);

include/linux/task_work.h

@@ -14,11 +14,14 @@ init_task_work(struct callback_head *twork, task_work_func_t func)
 }
 
 enum task_work_notify_mode {
-	TWA_NONE,
+	TWA_NONE = 0,
 	TWA_RESUME,
 	TWA_SIGNAL,
 	TWA_SIGNAL_NO_IPI,
 	TWA_NMI_CURRENT,
+
+	TWA_FLAGS = 0xff00,
+	TWAF_NO_ALLOC = 0x0100,
 };
 
 static inline bool task_work_pending(struct task_struct *task)

kernel/events/core.c

@@ -9251,7 +9251,7 @@ static void perf_event_switch(struct task_struct *task,
 		},
 	};
 
-	if (!sched_in && task->on_rq) {
+	if (!sched_in && task_is_runnable(task)) {
 		switch_event.event_id.header.misc |=
 				PERF_RECORD_MISC_SWITCH_OUT_PREEMPT;
 	}

kernel/freezer.c

@@ -109,7 +109,12 @@ static int __set_task_frozen(struct task_struct *p, void *arg)
 {
 	unsigned int state = READ_ONCE(p->__state);
 
-	if (p->on_rq)
+	/*
+	 * Allow freezing the sched_delayed tasks; they will not execute until
+	 * ttwu() fixes them up, so it is safe to swap their state now, instead
+	 * of waiting for them to get fully dequeued.
+	 */
+	if (task_is_runnable(p))
 		return 0;
 
 	if (p != current && task_curr(p))

kernel/rcu/tasks.h

@@ -985,6 +985,15 @@ static bool rcu_tasks_is_holdout(struct task_struct *t)
 	if (!READ_ONCE(t->on_rq))
 		return false;
 
+	/*
+	 * t->on_rq && !t->se.sched_delayed *could* be considered sleeping but
+	 * since it is a spurious state (it will transition into the
+	 * traditional blocked state or get woken up without outside
+	 * dependencies), not considering it such should only affect timing.
+	 *
+	 * Be conservative for now and not include it.
+	 */
+
 	/*
 	 * Idle tasks (or idle injection) within the idle loop are RCU-tasks
 	 * quiescent states. But CPU boot code performed by the idle task

kernel/sched/core.c

@@ -548,6 +548,11 @@ sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
  *   ON_RQ_MIGRATING state is used for migration without holding both
  *   rq->locks. It indicates task_cpu() is not stable, see task_rq_lock().
  *
+ *   Additionally it is possible to be ->on_rq but still be considered not
+ *   runnable when p->se.sched_delayed is true. These tasks are on the runqueue
+ *   but will be dequeued as soon as they get picked again. See the
+ *   task_is_runnable() helper.
+ *
  * p->on_cpu <- { 0, 1 }:
  *
  *   is set by prepare_task() and cleared by finish_task() such that it will be
@@ -2012,11 +2017,6 @@ void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 	if (!(flags & ENQUEUE_NOCLOCK))
 		update_rq_clock(rq);
 
-	if (!(flags & ENQUEUE_RESTORE)) {
-		sched_info_enqueue(rq, p);
-		psi_enqueue(p, (flags & ENQUEUE_WAKEUP) && !(flags & ENQUEUE_MIGRATED));
-	}
-
 	p->sched_class->enqueue_task(rq, p, flags);
 	/*
 	 * Must be after ->enqueue_task() because ENQUEUE_DELAYED can clear
@@ -2024,6 +2024,11 @@ void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 	 */
 	uclamp_rq_inc(rq, p);
 
+	if (!(flags & ENQUEUE_RESTORE)) {
+		sched_info_enqueue(rq, p);
+		psi_enqueue(p, flags & ENQUEUE_MIGRATED);
+	}
+
 	if (sched_core_enabled(rq))
 		sched_core_enqueue(rq, p);
 }
@@ -2041,7 +2046,7 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 
 	if (!(flags & DEQUEUE_SAVE)) {
 		sched_info_dequeue(rq, p);
-		psi_dequeue(p, flags & DEQUEUE_SLEEP);
+		psi_dequeue(p, !(flags & DEQUEUE_SLEEP));
 	}
 
 	/*
@@ -4323,9 +4328,10 @@ static bool __task_needs_rq_lock(struct task_struct *p)
  * @arg: Argument to function.
  *
  * Fix the task in it's current state by avoiding wakeups and or rq operations
- * and call @func(@arg) on it.  This function can use ->on_rq and task_curr()
+ * and call @func(@arg) on it.  This function can use task_is_runnable() and
- * to work out what the state is, if required.  Given that @func can be invoked
+ * task_curr() to work out what the state is, if required.  Given that @func
- * with a runqueue lock held, it had better be quite lightweight.
+ * can be invoked with a runqueue lock held, it had better be quite
+ * lightweight.
  *
  * Returns:
  *   Whatever @func returns
@@ -6544,6 +6550,7 @@ static void __sched notrace __schedule(int sched_mode)
 	 * as a preemption by schedule_debug() and RCU.
 	 */
 	bool preempt = sched_mode > SM_NONE;
+	bool block = false;
 	unsigned long *switch_count;
 	unsigned long prev_state;
 	struct rq_flags rf;
@@ -6629,6 +6636,7 @@ static void __sched notrace __schedule(int sched_mode)
 			 * After this, schedule() must not care about p->state any more.
 			 */
 			block_task(rq, prev, flags);
+			block = true;
 		}
 		switch_count = &prev->nvcsw;
 	}
@@ -6674,7 +6682,7 @@ static void __sched notrace __schedule(int sched_mode)
 
 		migrate_disable_switch(rq, prev);
 		psi_account_irqtime(rq, prev, next);
-		psi_sched_switch(prev, next, !task_on_rq_queued(prev));
+		psi_sched_switch(prev, next, block);
 
 		trace_sched_switch(preempt, prev, next, prev_state);
 
@@ -7017,20 +7025,20 @@ int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flag
 }
 EXPORT_SYMBOL(default_wake_function);
 
-void __setscheduler_prio(struct task_struct *p, int prio)
+const struct sched_class *__setscheduler_class(struct task_struct *p, int prio)
 {
 	if (dl_prio(prio))
-		p->sched_class = &dl_sched_class;
+		return &dl_sched_class;
-	else if (rt_prio(prio))
-		p->sched_class = &rt_sched_class;
-#ifdef CONFIG_SCHED_CLASS_EXT
-	else if (task_should_scx(p))
-		p->sched_class = &ext_sched_class;
-#endif
-	else
-		p->sched_class = &fair_sched_class;
 
-	p->prio = prio;
+	if (rt_prio(prio))
+		return &rt_sched_class;
+
+#ifdef CONFIG_SCHED_CLASS_EXT
+	if (task_should_scx(p))
+		return &ext_sched_class;
+#endif
+
+	return &fair_sched_class;
 }
 
 #ifdef CONFIG_RT_MUTEXES
@@ -7076,7 +7084,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 {
 	int prio, oldprio, queued, running, queue_flag =
 		DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
-	const struct sched_class *prev_class;
+	const struct sched_class *prev_class, *next_class;
 	struct rq_flags rf;
 	struct rq *rq;
 
@@ -7134,6 +7142,11 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 		queue_flag &= ~DEQUEUE_MOVE;
 
 	prev_class = p->sched_class;
+	next_class = __setscheduler_class(p, prio);
+
+	if (prev_class != next_class && p->se.sched_delayed)
+		dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
+
 	queued = task_on_rq_queued(p);
 	running = task_current(rq, p);
 	if (queued)
@@ -7171,7 +7184,9 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 			p->rt.timeout = 0;
 	}
 
-	__setscheduler_prio(p, prio);
+	p->sched_class = next_class;
+	p->prio = prio;
+
 	check_class_changing(rq, p, prev_class);
 
 	if (queued)
@@ -10465,7 +10480,9 @@ void task_tick_mm_cid(struct rq *rq, struct task_struct *curr)
 		return;
 	if (time_before(now, READ_ONCE(curr->mm->mm_cid_next_scan)))
 		return;
-	task_work_add(curr, work, TWA_RESUME);
+
+	/* No page allocation under rq lock */
+	task_work_add(curr, work, TWA_RESUME | TWAF_NO_ALLOC);
 }
 
 void sched_mm_cid_exit_signals(struct task_struct *t)

kernel/sched/deadline.c

@@ -2385,7 +2385,7 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
 
 	deadline_queue_push_tasks(rq);
 
-	if (hrtick_enabled(rq))
+	if (hrtick_enabled_dl(rq))
 		start_hrtick_dl(rq, &p->dl);
 }
 

kernel/sched/ext.c

@@ -4493,7 +4493,7 @@ static void scx_ops_disable_workfn(struct kthread_work *work)
 
 		sched_deq_and_put_task(p, DEQUEUE_SAVE | DEQUEUE_MOVE, &ctx);
 
-		__setscheduler_prio(p, p->prio);
+		p->sched_class = __setscheduler_class(p, p->prio);
 		check_class_changing(task_rq(p), p, old_class);
 
 		sched_enq_and_set_task(&ctx);
@@ -5204,7 +5204,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
 		sched_deq_and_put_task(p, DEQUEUE_SAVE | DEQUEUE_MOVE, &ctx);
 
 		p->scx.slice = SCX_SLICE_DFL;
-		__setscheduler_prio(p, p->prio);
+		p->sched_class = __setscheduler_class(p, p->prio);
 		check_class_changing(task_rq(p), p, old_class);
 
 		sched_enq_and_set_task(&ctx);

kernel/sched/fair.c

@@ -1247,7 +1247,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
 
 	account_cfs_rq_runtime(cfs_rq, delta_exec);
 
-	if (rq->nr_running == 1)
+	if (cfs_rq->nr_running == 1)
 		return;
 
 	if (resched || did_preempt_short(cfs_rq, curr)) {
@@ -6058,10 +6058,13 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	for_each_sched_entity(se) {
 		struct cfs_rq *qcfs_rq = cfs_rq_of(se);
 
-		if (se->on_rq) {
+		/* Handle any unfinished DELAY_DEQUEUE business first. */
-			SCHED_WARN_ON(se->sched_delayed);
+		if (se->sched_delayed) {
+			int flags = DEQUEUE_SLEEP | DEQUEUE_DELAYED;
+
+			dequeue_entity(qcfs_rq, se, flags);
+		} else if (se->on_rq)
 			break;
-		}
 		enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);
 
 		if (cfs_rq_is_idle(group_cfs_rq(se)))
@@ -13174,22 +13177,6 @@ static void attach_task_cfs_rq(struct task_struct *p)
 static void switched_from_fair(struct rq *rq, struct task_struct *p)
 {
 	detach_task_cfs_rq(p);
-	/*
-	 * Since this is called after changing class, this is a little weird
-	 * and we cannot use DEQUEUE_DELAYED.
-	 */
-	if (p->se.sched_delayed) {
-		/* First, dequeue it from its new class' structures */
-		dequeue_task(rq, p, DEQUEUE_NOCLOCK | DEQUEUE_SLEEP);
-		/*
-		 * Now, clean up the fair_sched_class side of things
-		 * related to sched_delayed being true and that wasn't done
-		 * due to the generic dequeue not using DEQUEUE_DELAYED.
-		 */
-		finish_delayed_dequeue_entity(&p->se);
-		p->se.rel_deadline = 0;
-		__block_task(rq, p);
-	}
 }
 
 static void switched_to_fair(struct rq *rq, struct task_struct *p)

kernel/sched/sched.h

@@ -3800,7 +3800,7 @@ static inline int rt_effective_prio(struct task_struct *p, int prio)
 
 extern int __sched_setscheduler(struct task_struct *p, const struct sched_attr *attr, bool user, bool pi);
 extern int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx);
-extern void __setscheduler_prio(struct task_struct *p, int prio);
+extern const struct sched_class *__setscheduler_class(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 bool dequeue_task(struct rq *rq, struct task_struct *p, int flags);

kernel/sched/stats.h

@@ -119,45 +119,63 @@ static inline void psi_account_irqtime(struct rq *rq, struct task_struct *curr,
 /*
  * PSI tracks state that persists across sleeps, such as iowaits and
  * memory stalls. As a result, it has to distinguish between sleeps,
- * where a task's runnable state changes, and requeues, where a task
+ * where a task's runnable state changes, and migrations, where a task
- * and its state are being moved between CPUs and runqueues.
+ * and its runnable state are being moved between CPUs and runqueues.
+ *
+ * A notable case is a task whose dequeue is delayed. PSI considers
+ * those sleeping, but because they are still on the runqueue they can
+ * go through migration requeues. In this case, *sleeping* states need
+ * to be transferred.
  */
-static inline void psi_enqueue(struct task_struct *p, bool wakeup)
+static inline void psi_enqueue(struct task_struct *p, bool migrate)
 {
-	int clear = 0, set = TSK_RUNNING;
+	int clear = 0, set = 0;
 
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	if (p->in_memstall)
+	if (p->se.sched_delayed) {
-		set |= TSK_MEMSTALL_RUNNING;
+		/* CPU migration of "sleeping" task */
-
+		SCHED_WARN_ON(!migrate);
-	if (!wakeup) {
 		if (p->in_memstall)
 			set |= TSK_MEMSTALL;
+		if (p->in_iowait)
+			set |= TSK_IOWAIT;
+	} else if (migrate) {
+		/* CPU migration of runnable task */
+		set = TSK_RUNNING;
+		if (p->in_memstall)
+			set |= TSK_MEMSTALL | TSK_MEMSTALL_RUNNING;
 	} else {
+		/* Wakeup of new or sleeping task */
 		if (p->in_iowait)
 			clear |= TSK_IOWAIT;
+		set = TSK_RUNNING;
+		if (p->in_memstall)
+			set |= TSK_MEMSTALL_RUNNING;
 	}
 
 	psi_task_change(p, clear, set);
 }
 
-static inline void psi_dequeue(struct task_struct *p, bool sleep)
+static inline void psi_dequeue(struct task_struct *p, bool migrate)
 {
 	if (static_branch_likely(&psi_disabled))
 		return;
 
+	/*
+	 * When migrating a task to another CPU, clear all psi
+	 * state. The enqueue callback above will work it out.
+	 */
+	if (migrate)
+		psi_task_change(p, p->psi_flags, 0);
+
 	/*
 	 * A voluntary sleep is a dequeue followed by a task switch. To
 	 * avoid walking all ancestors twice, psi_task_switch() handles
 	 * TSK_RUNNING and TSK_IOWAIT for us when it moves TSK_ONCPU.
 	 * Do nothing here.
 	 */
-	if (sleep)
-		return;
-
-	psi_task_change(p, p->psi_flags, 0);
 }
 
 static inline void psi_ttwu_dequeue(struct task_struct *p)
@@ -190,8 +208,8 @@ static inline void psi_sched_switch(struct task_struct *prev,
 }
 
 #else /* CONFIG_PSI */
-static inline void psi_enqueue(struct task_struct *p, bool wakeup) {}
+static inline void psi_enqueue(struct task_struct *p, bool migrate) {}
-static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
+static inline void psi_dequeue(struct task_struct *p, bool migrate) {}
 static inline void psi_ttwu_dequeue(struct task_struct *p) {}
 static inline void psi_sched_switch(struct task_struct *prev,
 				    struct task_struct *next,

kernel/sched/syscalls.c

@@ -529,7 +529,7 @@ int __sched_setscheduler(struct task_struct *p,
 {
 	int oldpolicy = -1, policy = attr->sched_policy;
 	int retval, oldprio, newprio, queued, running;
-	const struct sched_class *prev_class;
+	const struct sched_class *prev_class, *next_class;
 	struct balance_callback *head;
 	struct rq_flags rf;
 	int reset_on_fork;
@@ -706,6 +706,12 @@ int __sched_setscheduler(struct task_struct *p,
 			queue_flags &= ~DEQUEUE_MOVE;
 	}
 
+	prev_class = p->sched_class;
+	next_class = __setscheduler_class(p, newprio);
+
+	if (prev_class != next_class && p->se.sched_delayed)
+		dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
+
 	queued = task_on_rq_queued(p);
 	running = task_current(rq, p);
 	if (queued)
@@ -713,11 +719,10 @@ int __sched_setscheduler(struct task_struct *p,
 	if (running)
 		put_prev_task(rq, p);
 
-	prev_class = p->sched_class;
-
 	if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
 		__setscheduler_params(p, attr);
-		__setscheduler_prio(p, newprio);
+		p->sched_class = next_class;
+		p->prio = newprio;
 	}
 	__setscheduler_uclamp(p, attr);
 	check_class_changing(rq, p, prev_class);

kernel/task_work.c

@@ -55,15 +55,26 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 		  enum task_work_notify_mode notify)
 {
 	struct callback_head *head;
+	int flags = notify & TWA_FLAGS;
 
+	notify &= ~TWA_FLAGS;
 	if (notify == TWA_NMI_CURRENT) {
 		if (WARN_ON_ONCE(task != current))
 			return -EINVAL;
 		if (!IS_ENABLED(CONFIG_IRQ_WORK))
 			return -EINVAL;
 	} else {
-		/* record the work call stack in order to print it in KASAN reports */
+		/*
-		kasan_record_aux_stack(work);
+		 * Record the work call stack in order to print it in KASAN
+		 * reports.
+		 *
+		 * Note that stack allocation can fail if TWAF_NO_ALLOC flag
+		 * is set and new page is needed to expand the stack buffer.
+		 */
+		if (flags & TWAF_NO_ALLOC)
+			kasan_record_aux_stack_noalloc(work);
+		else
+			kasan_record_aux_stack(work);
 	}
 
 	head = READ_ONCE(task->task_works);

kernel/time/tick-sched.c

@@ -434,6 +434,12 @@ static void tick_nohz_kick_task(struct task_struct *tsk)
 	 *   smp_mb__after_spin_lock()
 	 *   tick_nohz_task_switch()
 	 *     LOAD p->tick_dep_mask
+	 *
+	 * XXX given a task picks up the dependency on schedule(), should we
+	 * only care about tasks that are currently on the CPU instead of all
+	 * that are on the runqueue?
+	 *
+	 * That is, does this want to be: task_on_cpu() / task_curr()?
 	 */
 	if (!sched_task_on_rq(tsk))
 		return;

kernel/trace/trace_selftest.c

@@ -1485,7 +1485,7 @@ trace_selftest_startup_wakeup(struct tracer *trace, struct trace_array *tr)
 	/* reset the max latency */
 	tr->max_latency = 0;
 
-	while (p->on_rq) {
+	while (task_is_runnable(p)) {
 		/*
 		 * Sleep to make sure the -deadline thread is asleep too.
 		 * On virtual machines we can't rely on timings,

virt/kvm/kvm_main.c

@@ -6387,7 +6387,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 
 	WRITE_ONCE(vcpu->scheduled_out, true);
 
-	if (current->on_rq && vcpu->wants_to_run) {
+	if (task_is_runnable(current) && vcpu->wants_to_run) {
 		WRITE_ONCE(vcpu->preempted, true);
 		WRITE_ONCE(vcpu->ready, true);
 	}