linux-kernel - Re: [patch 38/44] posix-cpu-timers: Respect INFINITY for hard RTTIME limit

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Date:   Mon, 19 Aug 2019 22:29:13 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ingo Molnar <mingo@...nel.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [patch 38/44] posix-cpu-timers: Respect INFINITY for hard RTTIME
 limit

On Mon, 19 Aug 2019, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > The RTIME limit expiry code does not check the hard RTTIME limit for
> > INFINITY, i.e. being disabled.  Add it.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  kernel/time/posix-cpu-timers.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/kernel/time/posix-cpu-timers.c
> > +++ b/kernel/time/posix-cpu-timers.c
> > @@ -905,7 +905,7 @@ static void check_process_timers(struct
> >  		u64 softns, ptime = samples[CPUCLOCK_PROF];
> >  		unsigned long psecs = div_u64(ptime, NSEC_PER_SEC);
> >  
> > -		if (psecs >= hard) {
> > +		if (hard != RLIM_INFINITY && psecs >= hard) {
> >  			/*
> >  			 * At the hard limit, we just die.
> >  			 * No need to calculate anything else now.
> 
> Might make sense to mark this as a possible ABI change in the changelog: 
> if some weird code learned to rely on this (arguably broken) behavior 
> then the bug turned into an ABI.

Will do, though that would be really interesting to see the offending
case. That limit is in seconds and RLIM_INFINITY is at least INT_MAX which
means 68 years. :)

I stumbled over it when I tried to consolidate that duplicated code in that
area. I'll amend the changelog to be more clear.

Thanks,

	tglx