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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20091110182415.GB6066@dhcp-lab-161.englab.brq.redhat.com>
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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/