Messages in this thread | | | Subject | Re: [PATCH] sched/rt: Fix double enqueue caused by rt_effective_prio | From | Dietmar Eggemann <> | Date | Tue, 6 Jul 2021 16:48:56 +0200 |
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On 01/07/2021 11:14, Juri Lelli wrote: > Double enqueues in rt runqueues (list) have been reported while running > a simple test that spawns a number of threads doing a short sleep/run > pattern while being concurrently setscheduled between rt and fair class.
I tried to recreate this in rt-app (with `pi-mutex` resource and `pi_enabled=true` but I can't bring the system into hitting this warning.
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> diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 0c22cd026440..c84ac1d675f4 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6823,7 +6823,8 @@ static void __setscheduler_params(struct task_struct *p, > > /* Actually do priority change: must hold pi & rq lock. */ > static void __setscheduler(struct rq *rq, struct task_struct *p, > - const struct sched_attr *attr, bool keep_boost) > + const struct sched_attr *attr, bool keep_boost, > + int new_effective_prio) > { > /* > * If params can't change scheduling class changes aren't allowed > @@ -6840,7 +6841,7 @@ static void __setscheduler(struct rq *rq, struct task_struct *p, > */ > p->prio = normal_prio(p); > if (keep_boost) > - p->prio = rt_effective_prio(p, p->prio); > + p->prio = new_effective_prio;
So in case __sched_setscheduler() is called for p (SCHED_NORMAL, NICE0) you want to avoid that this 2. rt_effective_prio() call returns p->prio=120 in case the 1. call (in __sched_setscheduler()) did return 0 (due to pi_task->prio=0 (FIFO rt_priority=99 task))?
> > if (dl_prio(p->prio)) > p->sched_class = &dl_sched_class; > @@ -6873,7 +6874,7 @@ static int __sched_setscheduler(struct task_struct *p, > int newprio = dl_policy(attr->sched_policy) ? MAX_DL_PRIO - 1 : > MAX_RT_PRIO - 1 - attr->sched_priority; > int retval, oldprio, oldpolicy = -1, queued, running; > - int new_effective_prio, policy = attr->sched_policy; > + int new_effective_prio = newprio, policy = attr->sched_policy; > const struct sched_class *prev_class; > struct callback_head *head; > struct rq_flags rf; > @@ -7072,6 +7073,9 @@ static int __sched_setscheduler(struct task_struct *p, > oldprio = p->prio; > > if (pi) { > + newprio = fair_policy(attr->sched_policy) ? > + NICE_TO_PRIO(attr->sched_nice) : newprio; > +
Why is this necessary? p (SCHED_NORMAL) would get newprio=99 now and with this it gets [100...120...139] which is still greater than any RT (0-98)/DL (-1) prio?
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