linux-kernel - Re: [LTP] [PATCH] sched/rt: Disallow writing invalid values to sched_rt_period

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Date:   Fri, 22 Sep 2023 13:43:26 +0200
From:   Cyril Hrubis <chrubis@...e.cz>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Petr Vorel <pvorel@...e.cz>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, ltp@...ts.linux.it
Subject: Re: [LTP] [PATCH] sched/rt: Disallow writing invalid values to
 sched_rt_period_us

Hi!
> > > Documentation/scheduller/sched-rt-group.rst [1] specifies this as values from -1 to
> > > (INT_MAX - 1), I guess due int range. Looking into proc_dointvec_minmax() [2]
> > > even INT_MAX would pass the check. I suppose we can do nothing about that,
> > > because there is no value in sysctl_vals[] which would represent INT_MAX - 1.
> > > 
> > > And you specify in LTP test range: from -1 to INT_MAX.
> > > 
> > > But even much shorter value than INT_MAX fails:
> > > 
> > > $ echo 1234567 > /proc/sys/kernel/sched_rt_runtime_us
> > > sh: echo: write error: Invalid argument
> > 
> > That is because runtime_us must be < period_us by definition, since
> > runtime_us defines how much time is allocated from the period_us. I
> > guess that this is not described good enough in the kernel docs.
> 
> Mind adding a second patch to your series, clarifying 
> Documentation/scheduler/sched-rt-group.rst?

Yes, that is the plan. I've been working on LTP release for past two
weeks so this has been postponed. I will get to it hopefully next week.

-- 
Cyril Hrubis
chrubis@...e.cz