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

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Message-ID: <ZPIqsmTbJh7z-LcO@yuki>
Date:   Fri, 1 Sep 2023 20:17:22 +0200
From:   Cyril Hrubis <chrubis@...e.cz>
To:     Petr Vorel <pvorel@...e.cz>
Cc:     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.

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