linux-kernel - Re: utime/stime decreasing on thread exit

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Date:	Tue, 10 Nov 2009 19:24:15 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Spencer Candland <spencer@...ehost.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: utime/stime decreasing on thread exit

On Tue, Nov 10, 2009 at 06:40:08PM +0100, Oleg Nesterov wrote:
> > One other exception is:
> > fastpath_timer_check() -> thread_group_cputimer() -> thread_group_cputime()
> >
> > We can solve this like that:
> >
> > --- a/kernel/posix-cpu-timers.c
> > +++ b/kernel/posix-cpu-timers.c
> > @@ -1375,13 +1375,8 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
> >  	}
> >
> >  	sig = tsk->signal;
> > -	if (!task_cputime_zero(&sig->cputime_expires)) {
> > -		struct task_cputime group_sample;
> > -
> > -		thread_group_cputimer(tsk, &group_sample);
> > -		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
> > -			return 1;
> > -	}
> > +	if (!task_cputime_zero(&sig->cputime_expires))
> > +		return 1;
> >
> >  	return sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY;
> >  }
> >
> > Or stay with task_cputime_expired() but only if cputimer is currently running.
> 
> Oh. I forgot this code completely, can't comment.
> 
> Can't we ensure that fastpath_timer_check() never do while_each_thread() ?

Removing possibility to call while_each_tread() from fastpath_timer_check()
was exactly my intension here, perhaps I was not clear.

> IOW, if sig->cputime_expires != 0 then ->running must be true.
> At least, shouldn't stop_process_timers() clear sig->cputime_expires ?

I'm going to think about that. However as far seems, checking ->running
explicitly and goto slow patch when is not true is safer solution.

Stanislaw
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