linux-kernel - Re: [PATCH] omit POSIX timer stuff from task

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Message-ID: <alpine.LFD.2.20.1701201741110.2671@knanqh.ubzr>
Date:   Fri, 20 Jan 2017 17:46:33 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     John Stultz <john.stultz@...aro.org>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] omit POSIX timer stuff from task_struct when disabled

On Fri, 20 Jan 2017, John Stultz wrote:

> On Mon, Jan 9, 2017 at 10:49 AM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> > When CONFIG_POSIX_TIMERS is disabled, it is preferable to remove related
> > structures from struct task_struct and struct signal_struct as they
> > won't contain anything useful and shouldn't be relied upon by mistake.
> > Code still referencing those structures is also disabled here.
> >
> > Signed-off-by: Nicolas Pitre <nico@...aro.org>
> >
> [snip]
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 11c5c8ab82..8e333e55a9 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -1309,6 +1309,7 @@ void __cleanup_sighand(struct sighand_struct *sighand)
> >   */
> >  static void posix_cpu_timers_init_group(struct signal_struct *sig)
> >  {
> > +#ifdef CONFIG_POSIX_TIMERS
> >         unsigned long cpu_limit;
> >
> >         cpu_limit = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
> > @@ -1321,6 +1322,7 @@ static void posix_cpu_timers_init_group(struct signal_struct *sig)
> >         INIT_LIST_HEAD(&sig->cpu_timers[0]);
> >         INIT_LIST_HEAD(&sig->cpu_timers[1]);
> >         INIT_LIST_HEAD(&sig->cpu_timers[2]);
> > +#endif
> >  }
> 
> So apologies for not catching this earlier. I was just queuing this
> up, when I noticed the style issue here.
> 
> Aren't in-function ifdefs frowned upon? Wouldn't it be better to do:
> #ifdef CONFIG_POSIX_TIMERS
> static void posix_cpu_timers_init_group(struct signal_struct *sig)
> {
> ...
> }
> #else
> static void posix_cpu_timers_init_group(struct signal_struct *sig) {}
> #endif
> 
> And similar for most of the ifdef'ed out functions in this patch?

Well... I don't mind either ways.  In this case those functions are 
rather small and doing it the way you suggest doubles the number of 
added lines in this hunk. That's why I opted for the current style.

Just tell me if you prefer that I respin the patch and I'll do it.


Nicolas