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

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Message-ID: <20131216222051.GA21056@madcap2.tricolour.ca>
Date:	Mon, 16 Dec 2013 17:20:51 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-audit@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 11/12] pid: rewrite task helper functions avoiding
 task->pid and task->tgid

On 13/12/16, Oleg Nesterov wrote:
> Hi Richard,
> 
> Sorry, I already forgot the context, not sure I understand your email
> correctly.
> 
> On 12/16, Richard Guy Briggs wrote:
> > On 13/08/26, Richard Guy Briggs wrote:
> > > On Thu, Aug 22, 2013 at 09:08:48PM +0200, Oleg Nesterov wrote:
> > > > On 08/20, Richard Guy Briggs wrote:
> > > > >
> > > > >  static inline int is_global_init(struct task_struct *tsk)
> > > > >  {
> > > > > -	return tsk->pid == 1;
> > > > > +	return task_pid_nr(tsk) == 1;
> > > > >  }
> > > >
> > > > Probably it would be better to simply kill it. Almost every usage is
> > > > wrong.
> > >
> > > Can you be more clear?  I don't follow.  It should instead return a
> > > boolean.  Usage of is_global_init() or task_pid_nr()?
> > >
> > > If is_global_init(), is that because they could be unaware of pid
> > > namespaces?
> > >
> > > If task_pid_nr(), is that for the same reason?
> >
> > Oleg,  I still don't understand your comment above.  Kill what,
> > "is_global_init()"?  If so, how is almost every usage of it wrong?
> 
> Because is_global_init() is only true for the main thread of /sbin/init.
> 
> Just look at oom_unkillable_task(). It tries to not kill init. But, say,
> select_bad_process() can happily find a sub-thread of is_global_init()
> and still kill it.

Ah!  So it should be task_tgid_nr(tsk) == 1.

> > There are a number of functions that call is_global_init().  Might any
> > of them be called from inside the namespace context of a container and
> > hence should return true?
> 
> Not sure I understand, but certainly some callers should check ->child_reaper
> or SIGNAL_UNKILLABLE instead. Say, unhandled_signal().

So in some situations it should allow it to kill init of a container and
in others, refuse it.

> > > > >  static inline bool is_idle_task(const struct task_struct *p)
> > > > >  {
> > > > > -	return p->pid == 0;
> > > > > +	return task_pid(p) == &init_struct_pid;
> > > > >  }
> > > >
> > > > hmm. there should be a simpler check for this...
> > >
> > > Other than the original, this one is pretty simple.  What did you have
> > > in mind?
> >
> > I vaguely remember a clarification to this, but don't remember and can't
> > find it.  What sort of simplification did you have in mind?
> 
> I do not remember ;) Most probably, I meant "it would be nice to find a
> simpler check".

I'll stick with task_pid_nr(p) == 0.

> Oleg.

- RGB

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