linux-kernel - Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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:	Tue, 16 Nov 2010 07:18:29 -0700
From:	Mike Galbraith <efault@....de>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

On Tue, 2010-11-16 at 14:04 +0100, Oleg Nesterov wrote:
> On 11/15, Mike Galbraith wrote:
> >
> > On Mon, 2010-11-15 at 13:57 +0100, Oleg Nesterov wrote:
> >
> > > And the exiting task can do a lot before it disappears, probably
> > > we shouldn't ignore ->autogroup.
> 
> I don't really understand what makes the exiting task different,
> but OK.
> 
> However, I must admit I dislike this check. Because, looking at this
> code, it is not clear why do we check PF_EXITING. It looks as if it
> is needed for correctness.

Is _not_ needed I presume.

I'll remove it, I'm not overly attached (a t t a..;) to it. 

> OK, this is minor. I think the patch is correct, just one nit below.
> 
> > > It can't protect the change of signal->autogroup, multiple callers
> > > can use different rq's.
> >
> > Guaranteed live ->autogroup should be good enough for heuristic use, and
> > had better be so.  Having to take ->siglock in the fast path would kill
> > using ->signal.
> 
> Yes, sure, rq->lock should ensure signal->autogroup can't go away.
> (even if it can be changed under us). And it does, we are moving all
> threads before kref_put().

(yeah)

> > +static void
> > +autogroup_move_group(struct task_struct *p, struct autogroup *ag)
> > +{
> > +	struct autogroup *prev;
> > +	struct task_struct *t;
> > +
> > +	prev = p->signal->autogroup;
> > +	if (prev == ag)
> > +		return;
> > +
> > +	p->signal->autogroup = autogroup_kref_get(ag);
> > +	sched_move_task(p);
> > +
> > +	rcu_read_lock();
> > +	list_for_each_entry_rcu(t, &p->thread_group, thread_group) {
> > +		sched_move_task(t);
> > +	}
> > +	rcu_read_unlock();
> > +
> > +	autogroup_kref_put(prev);
> > +}
> 
> Well, this looks a bit strange (but correct).

My mouse copied it.

> We are changing ->autogroup assuming the caller holds ->siglock.
> But if we hold ->siglock we do not need rcu_read_lock() to iterate
> over the thread_group, we can just do
> 
> 	p->signal->autogroup = autogroup_kref_get(ag);
> 
> 	t = p;
> 	do {
> 		sched_move_task(t);
> 	} while_each_thread(p, t);
> 
> Again, this is minor, I won't insist.

I'll do it that way.  I was pondering adding the option to move one or
all as cgroups does, but don't think that will ever be needed.

	Thanks,

	-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/