Commit 083fc6d7 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'sched-urgent-2025-09-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull scheduler fixes from Ingo Molnar:
 "Fix two dl_server regressions: a race that can end up leaving the
  dl_server stuck, and a dl_server throttling bug causing lag to fair
  tasks"

* tag 'sched-urgent-2025-09-26' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/deadline: Fix dl_server behaviour
  sched/deadline: Fix dl_server getting stuck
parents 2cea0ed9 a3a70caf

include/linux/sched.h

+0 −2
Original line number Diff line number Diff line
@@ -706,7 +706,6 @@ struct sched_dl_entity { 
	unsigned int			dl_defer	  : 1;

	unsigned int			dl_defer_armed	  : 1;

	unsigned int			dl_defer_running  : 1;

	unsigned int			dl_server_idle    : 1;



	/*

	 * Bandwidth enforcement timer. Each -deadline task has its
@@ -733,7 +732,6 @@ struct sched_dl_entity { 
	 * runnable task.

	 */

	struct rq			*rq;

	dl_server_has_tasks_f		server_has_tasks;

	dl_server_pick_f		server_pick_task;



#ifdef CONFIG_RT_MUTEXES

kernel/sched/deadline.c

+3 −32
Original line number Diff line number Diff line
@@ -875,7 +875,7 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se) 
	 */

	if (dl_se->dl_defer && !dl_se->dl_defer_running &&

	    dl_time_before(rq_clock(dl_se->rq), dl_se->deadline - dl_se->runtime)) {

		if (!is_dl_boosted(dl_se) && dl_se->server_has_tasks(dl_se)) {

		if (!is_dl_boosted(dl_se)) {



			/*

			 * Set dl_se->dl_defer_armed and dl_throttled variables to
@@ -1152,8 +1152,6 @@ static void __push_dl_task(struct rq *rq, struct rq_flags *rf) 
/* a defer timer will not be reset if the runtime consumed was < dl_server_min_res */

static const u64 dl_server_min_res = 1 * NSEC_PER_MSEC;



static bool dl_server_stopped(struct sched_dl_entity *dl_se);



static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_dl_entity *dl_se)

{

	struct rq *rq = rq_of_dl_se(dl_se);
@@ -1171,12 +1169,6 @@ static enum hrtimer_restart dl_server_timer(struct hrtimer *timer, struct sched_ 
		if (!dl_se->dl_runtime)

			return HRTIMER_NORESTART;



		if (!dl_se->server_has_tasks(dl_se)) {

			replenish_dl_entity(dl_se);

			dl_server_stopped(dl_se);

			return HRTIMER_NORESTART;

		}



		if (dl_se->dl_defer_armed) {

			/*

			 * First check if the server could consume runtime in background.
@@ -1579,11 +1571,9 @@ void dl_server_update_idle_time(struct rq *rq, struct task_struct *p) 
void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)

{

	/* 0 runtime = fair server disabled */

	if (dl_se->dl_runtime) {

		dl_se->dl_server_idle = 0;

	if (dl_se->dl_runtime)

		update_curr_dl_se(dl_se->rq, dl_se, delta_exec);

}

}



void dl_server_start(struct sched_dl_entity *dl_se)

{
@@ -1610,26 +1600,10 @@ void dl_server_stop(struct sched_dl_entity *dl_se) 
	dl_se->dl_server_active = 0;

}



static bool dl_server_stopped(struct sched_dl_entity *dl_se)

{

	if (!dl_se->dl_server_active)

		return true;



	if (dl_se->dl_server_idle) {

		dl_server_stop(dl_se);

		return true;

	}



	dl_se->dl_server_idle = 1;

	return false;

}



void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,

		    dl_server_has_tasks_f has_tasks,

		    dl_server_pick_f pick_task)

{

	dl_se->rq = rq;

	dl_se->server_has_tasks = has_tasks;

	dl_se->server_pick_task = pick_task;

}
@@ -2394,10 +2368,7 @@ static struct task_struct *__pick_task_dl(struct rq *rq) 
	if (dl_server(dl_se)) {

		p = dl_se->server_pick_task(dl_se);

		if (!p) {

			if (!dl_server_stopped(dl_se)) {

				dl_se->dl_yielded = 1;

				update_curr_dl_se(rq, dl_se, 0);

			}

			dl_server_stop(dl_se);

			goto again;

		}

		rq->dl_server = dl_se;

kernel/sched/fair.c

+1 −6
Original line number Diff line number Diff line
@@ -8859,11 +8859,6 @@ static struct task_struct *__pick_next_task_fair(struct rq *rq, struct task_stru 
	return pick_next_task_fair(rq, prev, NULL);

}



static bool fair_server_has_tasks(struct sched_dl_entity *dl_se)

{

	return !!dl_se->rq->cfs.nr_queued;

}



static struct task_struct *fair_server_pick_task(struct sched_dl_entity *dl_se)

{

	return pick_task_fair(dl_se->rq);
@@ -8875,7 +8870,7 @@ void fair_server_init(struct rq *rq) 


	init_dl_entity(dl_se);



	dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick_task);

	dl_server_init(dl_se, rq, fair_server_pick_task);

}



/*

kernel/sched/sched.h

+31 −6
Original line number Diff line number Diff line
@@ -365,25 +365,50 @@ extern s64 dl_scaled_delta_exec(struct rq *rq, struct sched_dl_entity *dl_se, s6 
 *

 *   dl_se::rq -- runqueue we belong to.

 *

 *   dl_se::server_has_tasks() -- used on bandwidth enforcement; we 'stop' the

 *                                server when it runs out of tasks to run.

 *

 *   dl_se::server_pick() -- nested pick_next_task(); we yield the period if this

 *                           returns NULL.

 *

 *   dl_server_update() -- called from update_curr_common(), propagates runtime

 *                         to the server.

 *

 *   dl_server_start()

 *   dl_server_stop()  -- start/stop the server when it has (no) tasks.

 *   dl_server_start() -- start the server when it has tasks; it will stop

 *			  automatically when there are no more tasks, per

 *			  dl_se::server_pick() returning NULL.

 *

 *   dl_server_stop() -- (force) stop the server; use when updating

 *                       parameters.

 *

 *   dl_server_init() -- initializes the server.

 *

 * When started the dl_server will (per dl_defer) schedule a timer for its

 * zero-laxity point -- that is, unlike regular EDF tasks which run ASAP, a

 * server will run at the very end of its period.

 *

 * This is done such that any runtime from the target class can be accounted

 * against the server -- through dl_server_update() above -- such that when it

 * becomes time to run, it might already be out of runtime and get deferred

 * until the next period. In this case dl_server_timer() will alternate

 * between defer and replenish but never actually enqueue the server.

 *

 * Only when the target class does not manage to exhaust the server's runtime

 * (there's actualy starvation in the given period), will the dl_server get on

 * the runqueue. Once queued it will pick tasks from the target class and run

 * them until either its runtime is exhaused, at which point its back to

 * dl_server_timer, or until there are no more tasks to run, at which point

 * the dl_server stops itself.

 *

 * By stopping at this point the dl_server retains bandwidth, which, if a new

 * task wakes up imminently (starting the server again), can be used --

 * subject to CBS wakeup rules -- without having to wait for the next period.

 *

 * Additionally, because of the dl_defer behaviour the start/stop behaviour is

 * naturally thottled to once per period, avoiding high context switch

 * workloads from spamming the hrtimer program/cancel paths.

 */

extern void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec);

extern void dl_server_start(struct sched_dl_entity *dl_se);

extern void dl_server_stop(struct sched_dl_entity *dl_se);

extern void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,

		    dl_server_has_tasks_f has_tasks,

		    dl_server_pick_f pick_task);

extern void sched_init_dl_servers(void);