linux-kernel - Re: [PATCH v2 2/3] time,signal: protect resource use statistics with seqlock

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]

Date:	Mon, 18 Aug 2014 06:44:49 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, fweisbec@...il.com,
	akpm@...ux-foundation.org, srao@...hat.com, lwoodman@...hat.com,
	atheurer@...hat.com
Subject: Re: [PATCH v2 2/3] time,signal: protect resource use statistics
 with seqlock

On Sat, 2014-08-16 at 19:50 +0200, Oleg Nesterov wrote: 
> On 08/16, Rik van Riel wrote:
> >
> > +	do {
> > +		seq = nextseq;
> > +		read_seqbegin_or_lock(&sig->stats_lock, &seq);
> > +		times->utime = sig->utime;
> > +		times->stime = sig->stime;
> > +		times->sum_exec_runtime = sig->sum_sched_runtime;
> > +
> > +		for_each_thread(tsk, t) {
> > +			task_cputime(t, &utime, &stime);
> > +			times->utime += utime;
> > +			times->stime += stime;
> > +			times->sum_exec_runtime += task_sched_runtime(t);
> > +		}
> > +		/* If lockless access failed, take the lock. */
> > +		nextseq = 1;
> 
> Yes, thanks, this answers my concerns.
> 
> Cough... can't resist, and I still think that we should take rcu_read_lock()
> only around for_each_thread() and the patch expands the critical section for
> no reason. But this is minor, I won't insist.

Hm.  Should traversal not also disable preemption to preserve the error
bound Peter mentioned?

-Mike

--
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/