Re: [PATCH] sched: Avoid spurious lock dependencies

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

> Subject: sched: Avoid spurious lock dependencies
> 
> While seemingly harmless, __sched_fork() does hrtimer_init(), which,
> when DEBUG_OBJETS, can end up doing allocations.
> 

NIT: s/DEBUG_OBJETS/DEBUG_OBJECTS

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7880f4f64d0e..1832fc0fbec5 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6039,10 +6039,11 @@ void init_idle(struct task_struct *idle, int cpu)
>  	struct rq *rq = cpu_rq(cpu);
>  	unsigned long flags;
>  
> +	__sched_fork(0, idle);
> +
>  	raw_spin_lock_irqsave(&idle->pi_lock, flags);
>  	raw_spin_lock(&rq->lock);
>  
> -	__sched_fork(0, idle);
>  	idle->state = TASK_RUNNING;
>  	idle->se.exec_start = sched_clock();
>  	idle->flags |= PF_IDLE;
> 

Given that there is a comment just after this which says
"init_task() gets called multiple times on a task",
should we add a check if rq->idle is present and bail out?

if (rq->idle) {
    raw_spin_unlock(&rq->lock);
    raw_spin_unlock_irqrestore(&idle->pi_lock, flags);
    return;
}

Also can we also move the above 3 statements before the lock?


-- 
Thanks and Regards
Srikar Dronamraju