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sched/rt: Fix PI handling vs. sched_setscheduler()

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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:

  c365c292d0 ("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@gmail.com>
Tested-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-01-18 15:27:07 +01:00 committed by Ingo Molnar
parent 41d9339733
commit ff77e46853
4 changed files with 113 additions and 50 deletions
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2
include/linux/sched.h
View File

@ -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

39
kernel/sched/core.c
View File

@ -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);
}

86
kernel/sched/rt.c
View File

@ -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);
}

36
kernel/sched/sched.h
View File

@ -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)