Commit d3296052 authored by Tejun Heo's avatar Tejun Heo Committed by Peter Zijlstra
Browse files

sched/fair: set_load_weight() must also call reweight_task() for SCHED_IDLE tasks 



When a task's weight is being changed, set_load_weight() is called with
@update_load set. As weight changes aren't trivial for the fair class,
set_load_weight() calls fair.c::reweight_task() for fair class tasks.

However, set_load_weight() first tests task_has_idle_policy() on entry and
skips calling reweight_task() for SCHED_IDLE tasks. This is buggy as
SCHED_IDLE tasks are just fair tasks with a very low weight and they would
incorrectly skip load, vlag and position updates.

Fix it by updating reweight_task() to take struct load_weight as idle weight
can't be expressed with prio and making set_load_weight() call
reweight_task() for SCHED_IDLE tasks too when @update_load is set.

Fixes: 9059393e ("sched/fair: Use reweight_entity() for set_user_nice()")
Suggested-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org # v4.15+
Link: http://lkml.kernel.org/r/20240624102331.GI31592@noisy.programming.kicks-ass.net
parent 0ec208ce

kernel/sched/core.c

+10 −13
Original line number Diff line number Diff line
@@ -1328,27 +1328,24 @@ int tg_nop(struct task_group *tg, void *data) 
void set_load_weight(struct task_struct *p, bool update_load)

{

	int prio = p->static_prio - MAX_RT_PRIO;

	struct load_weight *load = &p->se.load;

	struct load_weight lw;



	/*

	 * SCHED_IDLE tasks get minimal weight:

	 */

	if (task_has_idle_policy(p)) {

		load->weight = scale_load(WEIGHT_IDLEPRIO);

		load->inv_weight = WMULT_IDLEPRIO;

		return;

		lw.weight = scale_load(WEIGHT_IDLEPRIO);

		lw.inv_weight = WMULT_IDLEPRIO;

	} else {

		lw.weight = scale_load(sched_prio_to_weight[prio]);

		lw.inv_weight = sched_prio_to_wmult[prio];

	}



	/*

	 * SCHED_OTHER tasks have to update their load when changing their

	 * weight

	 */

	if (update_load && p->sched_class == &fair_sched_class) {

		reweight_task(p, prio);

	} else {

		load->weight = scale_load(sched_prio_to_weight[prio]);

		load->inv_weight = sched_prio_to_wmult[prio];

	}

	if (update_load && p->sched_class == &fair_sched_class)

		reweight_task(p, &lw);

	else

		p->se.load = lw;

}



#ifdef CONFIG_UCLAMP_TASK

kernel/sched/fair.c

+3 −4
Original line number Diff line number Diff line
@@ -3835,15 +3835,14 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, 
	}

}



void reweight_task(struct task_struct *p, int prio)

void reweight_task(struct task_struct *p, const struct load_weight *lw)

{

	struct sched_entity *se = &p->se;

	struct cfs_rq *cfs_rq = cfs_rq_of(se);

	struct load_weight *load = &se->load;

	unsigned long weight = scale_load(sched_prio_to_weight[prio]);



	reweight_entity(cfs_rq, se, weight);

	load->inv_weight = sched_prio_to_wmult[prio];

	reweight_entity(cfs_rq, se, lw->weight);

	load->inv_weight = lw->inv_weight;

}



static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

kernel/sched/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -2509,7 +2509,7 @@ extern void init_sched_dl_class(void); 
extern void init_sched_rt_class(void);

extern void init_sched_fair_class(void);



extern void reweight_task(struct task_struct *p, int prio);

extern void reweight_task(struct task_struct *p, const struct load_weight *lw);



extern void resched_curr(struct rq *rq);

extern void resched_cpu(int cpu);