linux-kernel - Re: [patch 6/6] posix-cpu-timers: Make PID=0 and PID=self handling consistent

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Date:   Mon, 23 Sep 2019 16:17:14 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 6/6] posix-cpu-timers: Make PID=0 and PID=self handling
 consistent

On Mon, 23 Sep 2019, Frederic Weisbecker wrote:

> On Thu, Sep 05, 2019 at 02:03:45PM +0200, Thomas Gleixner wrote:
> > If the PID encoded into the clock id is 0 then the target is either the
> > calling thread itself or the process to which it belongs.
> > 
> > If the current thread encodes its own PID on a process wide clock then
> > there is no reason not to treat it in the same way as the PID=0 case.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  kernel/time/posix-cpu-timers.c |    9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> > 
> > --- a/kernel/time/posix-cpu-timers.c
> > +++ b/kernel/time/posix-cpu-timers.c
> > @@ -90,7 +90,14 @@ static struct task_struct *lookup_task(c
> >  
> >  	} else {
> >  		/*
> > -		 * For processes require that p is group leader.
> > +		 * Timer is going to be attached to a process. If p is
> > +		 * current then treat it like the PID=0 case above.
> > +		 */
> > +		if (p == current)
> > +			return current->group_leader;
> > +
> > +		/*
> > +		 * For foreign processes require that p is group leader.
> >  		 */
> >  		if (!has_group_leader_pid(p))
> >  			return NULL;
> 
> So, right after you should have that:
> 
>                 if (same_thread_group(p, current))
>                         return p;
> 
> Which I suggested to convert as:
> 
>                 if (p == current)
>                         return p;

Indeed :)