linux-kernel - Re: [patch V2 38/38] posix-cpu-timers: Utilize timerqueue for storage

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Date:   Tue, 27 Aug 2019 08:08:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Christoph Hellwig <hch@....de>
Subject: Re: [patch V2 38/38] posix-cpu-timers: Utilize timerqueue for
 storage

On Tue, 27 Aug 2019, Frederic Weisbecker wrote:

> On Wed, Aug 21, 2019 at 09:09:25PM +0200, Thomas Gleixner wrote:
> >  /**
> > @@ -92,14 +130,10 @@ struct posix_cputimers {
> >  
> >  static inline void posix_cputimers_init(struct posix_cputimers *pct)
> >  {
> > -	pct->timers_active = 0;
> > -	pct->expiry_active = 0;
> 
> No more need to initialize these?
> 
> > +	memset(pct->bases, 0, sizeof(pct->bases));

memset() does that IIRC :)

> >  	pct->bases[0].nextevt = U64_MAX;
> >  	pct->bases[1].nextevt = U64_MAX;
> >  	pct->bases[2].nextevt = U64_MAX;
> > -	INIT_LIST_HEAD(&pct->bases[0].cpu_timers);
> > -	INIT_LIST_HEAD(&pct->bases[1].cpu_timers);
> > -	INIT_LIST_HEAD(&pct->bases[2].cpu_timers);
> >  }
> 
> [...]
> 
> > @@ -393,15 +395,15 @@ static int posix_cpu_timer_del(struct k_
> >  	sighand = lock_task_sighand(p, &flags);
> >  	if (unlikely(sighand == NULL)) {
> >  		/*
> > -		 * We raced with the reaping of the task.
> > -		 * The deletion should have cleared us off the list.
> > +		 * This raced with the reaping of the task. The exit cleanup
> > +		 * should have removed this timer from the timer queue.
> >  		 */
> > -		WARN_ON_ONCE(!list_empty(&timer->it.cpu.entry));
> > +		WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
> 
> Should we clear ctmr->head upon cleanup_timerqueue() ?

Probably.