Re: Question about prio_changed_dl()

From: luca abeni
Date: Fri Mar 04 2016 - 03:51:20 EST

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In reply to: Peter Zijlstra: "Re: Question about prio_changed_dl()"
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Hi Peter,

On Wed, 2 Mar 2016 20:02:58 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
[...]
> > +++ b/kernel/sched/core.c
> > @@ -4079,6 +4079,8 @@ change:
> > new_effective_prio =
> > rt_mutex_get_effective_prio(p, newprio); if (new_effective_prio ==
> > oldprio) { __setscheduler_params(p, attr);
> > + if (p->sched_class == &dl_sched_class)
> > + p->sched_class->prio_changed(rq,
> > p, oldprio); task_rq_unlock(rq, p, &flags);
> > return 0;
> > }
>
> That code no longer exists like that.
>
> Can you see if the below patch (which caused that) also fixes your
> problem?

Some quick tests show that your patch seems to solve this issue too...
So, I am using this one locally instead of my patch.

Thanks,
Luca

> ---
> commit ff77e468535987b3d21b7bd4da15608ea3ce7d0b
> Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Mon Jan 18 15:27:07 2016 +0100
>
> sched/rt: Fix PI handling vs. sched_setscheduler()
>
> Andrea Parri reported:
>
> > I found that the following scenario (with
> > CONFIG_RT_GROUP_SCHED=y) is not handled correctly:
> >
> > T1 (prio = 20)
> > lock(rtmutex);
> >
> > T2 (prio = 20)
> > blocks on rtmutex (rt_nr_boosted = 0 on T1's rq)
> >
> > T1 (prio = 20)
> > sys_set_scheduler(prio = 0)
> > [new_effective_prio == oldprio]
> > T1 prio = 20 (rt_nr_boosted = 0 on T1's rq)
> >
> > The last step is incorrect as T1 is now boosted (c.f.,
> > rt_se_boosted()); in particular, if we continue with
> >
> > T1 (prio = 20)
> > unlock(rtmutex)
> > wakeup(T2)
> > adjust_prio(T1)
> > [prio != rt_mutex_getprio(T1)]
> > dequeue(T1)
> > rt_nr_boosted = (unsigned long)(-1)
> > ...
> > T1 prio = 0
> >
> > then we end up leaving rt_nr_boosted in an "inconsistent" state.
> >
> > The simple program attached could reproduce the previous
> > scenario; note that, as a consequence of the presence of this
> > state, the "assertion"
> >
> > WARN_ON(!rt_nr_running && rt_nr_boosted)
> >
> > from dec_rt_group() may trigger.
>
> So normally we dequeue/enqueue tasks in sched_setscheduler(),
> which would ensure the accounting stays correct. However in the early
> PI path we fail to do so.
>
> So this was introduced at around v3.14, by:
>
> c365c292d059 ("sched: Consider pi boosting in setscheduler()")
>
> which fixed another problem exactly because that dequeue/enqueue,
> joy.
> Fix this by teaching rt about DEQUEUE_SAVE/ENQUEUE_RESTORE and
> have it preserve runqueue location with that option. This requires
> decoupling the on_rt_rq() state from being on the list.
>
> In order to allow for explicit movement during the SAVE/RESTORE,
> introduce {DE,EN}QUEUE_MOVE. We still must use SAVE/RESTORE in
> these cases to preserve other invariants.
>
> Respecting the SAVE/RESTORE flags also has the (nice) side-effect
> that things like sys_nice()/sys_sched_setaffinity() also do not
> reorder FIFO tasks (whereas they used to before this patch).
>
> Reported-by: Andrea Parri <parri.andrea@xxxxxxxxx>
> Tested-by: Andrea Parri <parri.andrea@xxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mike Galbraith <efault@xxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a292c4b7e94c..87e5f9886ac8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1293,6 +1293,8 @@ struct sched_rt_entity {
> unsigned long timeout;
> unsigned long watchdog_stamp;
> unsigned int time_slice;
> + unsigned short on_rq;
> + unsigned short on_list;
>
> struct sched_rt_entity *back;
> #ifdef CONFIG_RT_GROUP_SCHED
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 291552b4d8ee..bb565b4663c8 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2221,6 +2221,10 @@ static void __sched_fork(unsigned long
> clone_flags, struct task_struct *p) __dl_clear_params(p);
>
> INIT_LIST_HEAD(&p->rt.run_list);
> + p->rt.timeout = 0;
> + p->rt.time_slice = sched_rr_timeslice;
> + p->rt.on_rq = 0;
> + p->rt.on_list = 0;
>
> #ifdef CONFIG_PREEMPT_NOTIFIERS
> INIT_HLIST_HEAD(&p->preempt_notifiers);
> @@ -3531,7 +3535,7 @@ EXPORT_SYMBOL(default_wake_function);
> */
> void rt_mutex_setprio(struct task_struct *p, int prio)
> {
> - int oldprio, queued, running, enqueue_flag = ENQUEUE_RESTORE;
> + int oldprio, queued, running, queue_flag = DEQUEUE_SAVE |
> DEQUEUE_MOVE; struct rq *rq;
> const struct sched_class *prev_class;
>
> @@ -3559,11 +3563,15 @@ void rt_mutex_setprio(struct task_struct *p,
> int prio)
> trace_sched_pi_setprio(p, prio);
> oldprio = p->prio;
> +
> + if (oldprio == prio)
> + queue_flag &= ~DEQUEUE_MOVE;
> +
> prev_class = p->sched_class;
> queued = task_on_rq_queued(p);
> running = task_current(rq, p);
> if (queued)
> - dequeue_task(rq, p, DEQUEUE_SAVE);
> + dequeue_task(rq, p, queue_flag);
> if (running)
> put_prev_task(rq, p);
>
> @@ -3581,7 +3589,7 @@ void rt_mutex_setprio(struct task_struct *p,
> int prio) if (!dl_prio(p->normal_prio) ||
> (pi_task && dl_entity_preempt(&pi_task->dl,
> &p->dl))) { p->dl.dl_boosted = 1;
> - enqueue_flag |= ENQUEUE_REPLENISH;
> + queue_flag |= ENQUEUE_REPLENISH;
> } else
> p->dl.dl_boosted = 0;
> p->sched_class = &dl_sched_class;
> @@ -3589,7 +3597,7 @@ void rt_mutex_setprio(struct task_struct *p,
> int prio) if (dl_prio(oldprio))
> p->dl.dl_boosted = 0;
> if (oldprio < prio)
> - enqueue_flag |= ENQUEUE_HEAD;
> + queue_flag |= ENQUEUE_HEAD;
> p->sched_class = &rt_sched_class;
> } else {
> if (dl_prio(oldprio))
> @@ -3604,7 +3612,7 @@ void rt_mutex_setprio(struct task_struct *p,
> int prio) if (running)
> p->sched_class->set_curr_task(rq);
> if (queued)
> - enqueue_task(rq, p, enqueue_flag);
> + enqueue_task(rq, p, queue_flag);
>
> check_class_changed(rq, p, prev_class, oldprio);
> out_unlock:
> @@ -3960,6 +3968,7 @@ static int __sched_setscheduler(struct
> task_struct *p, const struct sched_class *prev_class;
> struct rq *rq;
> int reset_on_fork;
> + int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
>
> /* may grab non-irq protected spin_locks */
> BUG_ON(in_interrupt());
> @@ -4142,17 +4151,14 @@ static int __sched_setscheduler(struct
> task_struct *p,
> * itself.
> */
> new_effective_prio = rt_mutex_get_effective_prio(p,
> newprio);
> - if (new_effective_prio == oldprio) {
> - __setscheduler_params(p, attr);
> - task_rq_unlock(rq, p, &flags);
> - return 0;
> - }
> + if (new_effective_prio == oldprio)
> + queue_flags &= ~DEQUEUE_MOVE;
> }
>
> queued = task_on_rq_queued(p);
> running = task_current(rq, p);
> if (queued)
> - dequeue_task(rq, p, DEQUEUE_SAVE);
> + dequeue_task(rq, p, queue_flags);
> if (running)
> put_prev_task(rq, p);
>
> @@ -4162,15 +4168,14 @@ static int __sched_setscheduler(struct
> task_struct *p, if (running)
> p->sched_class->set_curr_task(rq);
> if (queued) {
> - int enqueue_flags = ENQUEUE_RESTORE;
> /*
> * We enqueue to tail when the priority of a task is
> * increased (user space view).
> */
> - if (oldprio <= p->prio)
> - enqueue_flags |= ENQUEUE_HEAD;
> + if (oldprio < p->prio)
> + queue_flags |= ENQUEUE_HEAD;
>
> - enqueue_task(rq, p, enqueue_flags);
> + enqueue_task(rq, p, queue_flags);
> }
>
> check_class_changed(rq, p, prev_class, oldprio);
> @@ -7958,7 +7963,7 @@ void sched_move_task(struct task_struct *tsk)
> queued = task_on_rq_queued(tsk);
>
> if (queued)
> - dequeue_task(rq, tsk, DEQUEUE_SAVE);
> + dequeue_task(rq, tsk, DEQUEUE_SAVE | DEQUEUE_MOVE);
> if (unlikely(running))
> put_prev_task(rq, tsk);
>
> @@ -7982,7 +7987,7 @@ void sched_move_task(struct task_struct *tsk)
> if (unlikely(running))
> tsk->sched_class->set_curr_task(rq);
> if (queued)
> - enqueue_task(rq, tsk, ENQUEUE_RESTORE);
> + enqueue_task(rq, tsk, ENQUEUE_RESTORE |
> ENQUEUE_MOVE);
> task_rq_unlock(rq, tsk, &flags);
> }
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 8ec86abe0ea1..406a9c20b210 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -436,7 +436,7 @@ static void dequeue_top_rt_rq(struct rt_rq
> *rt_rq);
> static inline int on_rt_rq(struct sched_rt_entity *rt_se)
> {
> - return !list_empty(&rt_se->run_list);
> + return rt_se->on_rq;
> }
>
> #ifdef CONFIG_RT_GROUP_SCHED
> @@ -482,8 +482,8 @@ static inline struct rt_rq *group_rt_rq(struct
> sched_rt_entity *rt_se) return rt_se->my_q;
> }
>
> -static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool
> head); -static void dequeue_rt_entity(struct sched_rt_entity *rt_se);
> +static void enqueue_rt_entity(struct sched_rt_entity *rt_se,
> unsigned int flags); +static void dequeue_rt_entity(struct
> sched_rt_entity *rt_se, unsigned int flags);
> static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
> {
> @@ -499,7 +499,7 @@ static void sched_rt_rq_enqueue(struct rt_rq
> *rt_rq) if (!rt_se)
> enqueue_top_rt_rq(rt_rq);
> else if (!on_rt_rq(rt_se))
> - enqueue_rt_entity(rt_se, false);
> + enqueue_rt_entity(rt_se, 0);
>
> if (rt_rq->highest_prio.curr < curr->prio)
> resched_curr(rq);
> @@ -516,7 +516,7 @@ static void sched_rt_rq_dequeue(struct rt_rq
> *rt_rq) if (!rt_se)
> dequeue_top_rt_rq(rt_rq);
> else if (on_rt_rq(rt_se))
> - dequeue_rt_entity(rt_se);
> + dequeue_rt_entity(rt_se, 0);
> }
>
> static inline int rt_rq_throttled(struct rt_rq *rt_rq)
> @@ -1166,7 +1166,30 @@ void dec_rt_tasks(struct sched_rt_entity
> *rt_se, struct rt_rq *rt_rq) dec_rt_group(rt_se, rt_rq);
> }
>
> -static void __enqueue_rt_entity(struct sched_rt_entity *rt_se, bool
> head) +/*
> + * Change rt_se->run_list location unless SAVE && !MOVE
> + *
> + * assumes ENQUEUE/DEQUEUE flags match
> + */
> +static inline bool move_entity(unsigned int flags)
> +{
> + if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) == DEQUEUE_SAVE)
> + return false;
> +
> + return true;
> +}
> +
> +static void __delist_rt_entity(struct sched_rt_entity *rt_se, struct
> rt_prio_array *array) +{
> + list_del_init(&rt_se->run_list);
> +
> + if (list_empty(array->queue + rt_se_prio(rt_se)))
> + __clear_bit(rt_se_prio(rt_se), array->bitmap);
> +
> + rt_se->on_list = 0;
> +}
> +
> +static void __enqueue_rt_entity(struct sched_rt_entity *rt_se,
> unsigned int flags) {
> struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
> struct rt_prio_array *array = &rt_rq->active;
> @@ -1179,26 +1202,37 @@ static void __enqueue_rt_entity(struct
> sched_rt_entity *rt_se, bool head)
> * get throttled and the current group doesn't have any other
> * active members.
> */
> - if (group_rq && (rt_rq_throttled(group_rq)
> || !group_rq->rt_nr_running))
> + if (group_rq && (rt_rq_throttled(group_rq)
> || !group_rq->rt_nr_running)) {
> + if (rt_se->on_list)
> + __delist_rt_entity(rt_se, array);
> return;
> + }
>
> - if (head)
> - list_add(&rt_se->run_list, queue);
> - else
> - list_add_tail(&rt_se->run_list, queue);
> - __set_bit(rt_se_prio(rt_se), array->bitmap);
> + if (move_entity(flags)) {
> + WARN_ON_ONCE(rt_se->on_list);
> + if (flags & ENQUEUE_HEAD)
> + list_add(&rt_se->run_list, queue);
> + else
> + list_add_tail(&rt_se->run_list, queue);
> +
> + __set_bit(rt_se_prio(rt_se), array->bitmap);
> + rt_se->on_list = 1;
> + }
> + rt_se->on_rq = 1;
>
> inc_rt_tasks(rt_se, rt_rq);
> }
>
> -static void __dequeue_rt_entity(struct sched_rt_entity *rt_se)
> +static void __dequeue_rt_entity(struct sched_rt_entity *rt_se,
> unsigned int flags) {
> struct rt_rq *rt_rq = rt_rq_of_se(rt_se);
> struct rt_prio_array *array = &rt_rq->active;
>
> - list_del_init(&rt_se->run_list);
> - if (list_empty(array->queue + rt_se_prio(rt_se)))
> - __clear_bit(rt_se_prio(rt_se), array->bitmap);
> + if (move_entity(flags)) {
> + WARN_ON_ONCE(!rt_se->on_list);
> + __delist_rt_entity(rt_se, array);
> + }
> + rt_se->on_rq = 0;
>
> dec_rt_tasks(rt_se, rt_rq);
> }
> @@ -1207,7 +1241,7 @@ static void __dequeue_rt_entity(struct
> sched_rt_entity *rt_se)
> * Because the prio of an upper entry depends on the lower
> * entries, we must remove entries top - down.
> */
> -static void dequeue_rt_stack(struct sched_rt_entity *rt_se)
> +static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned
> int flags) {
> struct sched_rt_entity *back = NULL;
>
> @@ -1220,31 +1254,31 @@ static void dequeue_rt_stack(struct
> sched_rt_entity *rt_se)
> for (rt_se = back; rt_se; rt_se = rt_se->back) {
> if (on_rt_rq(rt_se))
> - __dequeue_rt_entity(rt_se);
> + __dequeue_rt_entity(rt_se, flags);
> }
> }
>
> -static void enqueue_rt_entity(struct sched_rt_entity *rt_se, bool
> head) +static void enqueue_rt_entity(struct sched_rt_entity *rt_se,
> unsigned int flags) {
> struct rq *rq = rq_of_rt_se(rt_se);
>
> - dequeue_rt_stack(rt_se);
> + dequeue_rt_stack(rt_se, flags);
> for_each_sched_rt_entity(rt_se)
> - __enqueue_rt_entity(rt_se, head);
> + __enqueue_rt_entity(rt_se, flags);
> enqueue_top_rt_rq(&rq->rt);
> }
>
> -static void dequeue_rt_entity(struct sched_rt_entity *rt_se)
> +static void dequeue_rt_entity(struct sched_rt_entity *rt_se,
> unsigned int flags) {
> struct rq *rq = rq_of_rt_se(rt_se);
>
> - dequeue_rt_stack(rt_se);
> + dequeue_rt_stack(rt_se, flags);
>
> for_each_sched_rt_entity(rt_se) {
> struct rt_rq *rt_rq = group_rt_rq(rt_se);
>
> if (rt_rq && rt_rq->rt_nr_running)
> - __enqueue_rt_entity(rt_se, false);
> + __enqueue_rt_entity(rt_se, flags);
> }
> enqueue_top_rt_rq(&rq->rt);
> }
> @@ -1260,7 +1294,7 @@ enqueue_task_rt(struct rq *rq, struct
> task_struct *p, int flags) if (flags & ENQUEUE_WAKEUP)
> rt_se->timeout = 0;
>
> - enqueue_rt_entity(rt_se, flags & ENQUEUE_HEAD);
> + enqueue_rt_entity(rt_se, flags);
>
> if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
> enqueue_pushable_task(rq, p);
> @@ -1271,7 +1305,7 @@ static void dequeue_task_rt(struct rq *rq,
> struct task_struct *p, int flags) struct sched_rt_entity *rt_se =
> &p->rt;
> update_curr_rt(rq);
> - dequeue_rt_entity(rt_se);
> + dequeue_rt_entity(rt_se, flags);
>
> dequeue_pushable_task(rq, p);
> }
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 3dc7b8b3f94c..d3606e40ea0d 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1130,18 +1130,40 @@ static inline void finish_lock_switch(struct
> rq *rq, struct task_struct *prev) extern const int
> sched_prio_to_weight[40]; extern const u32 sched_prio_to_wmult[40];
>
> +/*
> + * {de,en}queue flags:
> + *
> + * DEQUEUE_SLEEP - task is no longer runnable
> + * ENQUEUE_WAKEUP - task just became runnable
> + *
> + * SAVE/RESTORE - an otherwise spurious dequeue/enqueue, done to
> ensure tasks
> + * are in a known state which allows modification.
> Such pairs
> + * should preserve as much state as possible.
> + *
> + * MOVE - paired with SAVE/RESTORE, explicitly does not preserve the
> location
> + * in the runqueue.
> + *
> + * ENQUEUE_HEAD - place at front of runqueue (tail if not
> specified)
> + * ENQUEUE_REPLENISH - CBS (replenish runtime and postpone deadline)
> + * ENQUEUE_WAKING - sched_class::task_waking was called
> + *
> + */
> +
> +#define DEQUEUE_SLEEP 0x01
> +#define DEQUEUE_SAVE 0x02 /* matches ENQUEUE_RESTORE
> */ +#define DEQUEUE_MOVE 0x04 /* matches ENQUEUE_MOVE
> */ +
> #define ENQUEUE_WAKEUP 0x01
> -#define ENQUEUE_HEAD 0x02
> +#define ENQUEUE_RESTORE 0x02
> +#define ENQUEUE_MOVE 0x04
> +
> +#define ENQUEUE_HEAD 0x08
> +#define ENQUEUE_REPLENISH 0x10
> #ifdef CONFIG_SMP
> -#define ENQUEUE_WAKING 0x04 /*
> sched_class::task_waking was called */ +#define
> ENQUEUE_WAKING 0x20 #else
> #define ENQUEUE_WAKING 0x00
> #endif
> -#define ENQUEUE_REPLENISH 0x08
> -#define ENQUEUE_RESTORE 0x10
> -
> -#define DEQUEUE_SLEEP 0x01
> -#define DEQUEUE_SAVE 0x02
>
> #define RETRY_TASK ((void *)-1UL)
>

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In reply to: Peter Zijlstra: "Re: Question about prio_changed_dl()"
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