linux-kernel - Re: [PATCH 11/12] pid: rewrite task helper functions avoiding task->pid and task->tgid

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Date:	Thu, 22 Aug 2013 17:43:47 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>, linux-audit@...hat.com,
	linux-kernel@...r.kernel.org
Cc:	Eric Paris <eparis@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 11/12] pid: rewrite task helper functions avoiding
 task->pid and task->tgid

On Thu, Aug 22, 2013 at 10:05:55PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 20, 2013 at 05:32:03PM -0400, Richard Guy Briggs wrote:
> > This stops these four task helper functions from using the deprecated and
> > error-prone task->pid and task->tgid.
> > 
> > (informed by ebiederman's ea5a4d01)
> > Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> > Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
> > ---
> >  include/linux/sched.h |    8 ++++----
> >  1 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 8e69807..46e739d 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1579,7 +1579,7 @@ static inline int pid_alive(struct task_struct *p)
> >   */
> >  static inline int is_global_init(struct task_struct *tsk)
> >  {
> > -	return tsk->pid == 1;
> > +	return task_pid_nr(tsk) == 1;
> >  }
> >  
> >  extern struct pid *cad_pid;
> > @@ -1930,7 +1930,7 @@ extern struct task_struct *idle_task(int cpu);
> >   */
> >  static inline bool is_idle_task(const struct task_struct *p)
> >  {
> > -	return p->pid == 0;
> > +	return task_pid(p) == &init_struct_pid;
> >  }
> >  extern struct task_struct *curr_task(int cpu);
> >  extern void set_curr_task(int cpu, struct task_struct *p);
> 
> Why would you ever want to do this? It just makes these tests more
> expensive for no gain what so ff'ing ever.

Backups are generally considered a good idea, but in this case, I'd
quote:
	"A man with one watch knows what time it is. A man with two is
	never certain."

Reminds me of the twist of a phrase frequently seen in the US gov:
	"Government Duplicity, Do Not Propagate"   ;-)


Can you suggest a safe way to live with this duplicity?


- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer
Kernel Security
AMER ENG Base Operating Systems
Remote, Ottawa, Canada
Voice: +1.647.777.2635
Internal: (81) 32635
Alt: +1.613.693.0684x3545
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