linux-kernel - Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:)

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Date:	Thu, 16 Jun 2011 17:27:33 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Greg Kurz <gkurz@...ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com, containers@...ts.osdl.org,
	akpm@...ux-foundation.org, xemul@...nvz.org
Subject: Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was
	Vpid:)

On 16/06/11 17:01 +0200, Greg Kurz wrote:
> On Thu, 2011-06-16 at 15:25 +0200, Louis Rilling wrote:
> > > Ok. You're right, the RCU grace period is just what I need to ensure
> > I
> > > won't dereference a stale pointer. So I don't even have to bother
> > with
> > > ->siglock and just check pid_alive() before peeking into
> > pid->numbers.
> > 
> > It ends like open-coding an optimized version of task_pid_vnr(). If
> > the
> > optimization is really important (I guess this depends on the depth of
> > recursive
> > pid namespaces), it would be better to re-write task_pid_vnr().
> > Otherwise, just
> > use task_pid_vnr() as it is.
> > 
> > Thanks,
> > 
> > Louis
> > 
> Hmm, sorry Louis but I'm looking for the pid number from the task active
> pid_ns (AKA. the return value of getpid() if called by this task), so
> task_pid_vnr() doesn't fit.

Yup, I should have somewhat recalled that _vnr() means "in the caller's pid
namespace". Sorry for the wrong argument.

> 
> About the open-coding argument, that's why I used task_pid_nr_ns() and
> task_active_pid_ns() at first...

Sure. I still think that if you end accessing pid->numbers[pid->level].nr, then
you're close to coding some (optimized) task_active_pid_nr() that could also be
used by getpid(), using some task_active_tgid_nr() instead of task_tgid_vnr().
Anyway, optimization is not a relevant point here AFAICS.

Thanks,

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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