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SubjectRe: update vruntime incorrectly When use rt_mutex
On Thu, Mar 15, 2018 at 03:36:10PM +0800, Kathleen Chang wrote:
> hi,
>
> We found the vruntime might update incorrectly when use rt_mutex.

That's nice, on what kernel?

Also, your email is very hard to make sense of.

> <<abnormal case>>
> When the Task is waking, update vruntime incorrectly.
> 1. When there is a CFS task (A) hold rt_mutex_lock and the state is
> TASK_WAKING (on_rq=0), a RT task (B) want to hold this rt_mutex_lock.
> Update vruntime incorrectly.
>
> RT task (B)
> rt_mutex_setprio (cfs->RT) -> Task is waking , and update
> vruntime
>
> queued = task_on_rq_queued(p); // task is waking, queued=0
> running = task_current(rq, p);
> if (queued) /* don't update vruntime here! */
> dequeue_task(rq, p, queue_flag);
> if (running)
> put_prev_task(rq, p);
>
> check_class_changed(rq, p, prev_class, oldprio); ->
> switched_from_fair ->
> detach_task_cfs_rq
> ( due to task is waking, and bypass
> vruntime-=cfs_rq.min_vruntime)
>
> static void detach_task_cfs_rq(struct task_struct *p)
> {
> struct sched_entity *se = &p->se;
> struct cfs_rq *cfs_rq = cfs_rq_of(se);
>
> if (!vruntime_normalized(p)) { // return 1, then p->state is
> TASK_WAKING
> /*
> * Fix up our vruntime so that the current sleep doesn't
> * cause 'unlimited' sleep bonus.
> */
> place_entity(cfs_rq, se, 0);
> check_vruntime(8, se, cfs_rq->min_vruntime);
> se->vruntime -= cfs_rq->min_vruntime;

So here we subtract min_vruntime,

> se->normalized = true;

this doesn't exist.. which makes me wonder what you're looking at,

> }
>
> detach_entity_cfs_rq(se);
> }
>
> // when p->state is TASK_WAKING, the task's vruntime is normalized
> static inline bool vruntime_normalized(struct task_struct *p)
> {
> .....
> if (!se->sum_exec_runtime || p->state == TASK_WAKING)
> return true;
>
> }
>
> 2. When the task (A) which holds the rt_muex_lock unlock the
> rt_mutex_lock.
> Task (A) must be on_rq=1
>
> rt_mutex_setprio (RT->CFS)
> if (queued)
> enqueue_task(rq, p, queue_flag); );
> /* vruntime += cfs_rq.min_vruntime */

And here we're adding min_vruntime.

> if (running)
> set_curr_task(rq, p);
>
> that result in vruntime accumulates

So what exactly is the problem?


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