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 16:13:25 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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 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;

Either way, you can now remove those lines.

And then:

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>