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

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Date:	Tue, 10 Nov 2009 18:40:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Stanislaw Gruszka <sgruszka@...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 11/10, Stanislaw Gruszka wrote:
>
>   10    129  mm/oom_kill.c <<badness>>
>              thread_group_cputime(p, &task_time);
>
> Not sure about 10 - oom killer.

Not sure too, but I don't think we should worry about badness().

> 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() ?
IOW, if sig->cputime_expires != 0 then ->running must be true.

At least, shouldn't stop_process_timers() clear sig->cputime_expires ?

Oleg.

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