linux-kernel - Re: [PATCH 6/6] psi: introduce psi monitor

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Date:   Mon, 17 Dec 2018 17:21:05 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>, lizefan@...wei.com,
        Johannes Weiner <hannes@...xchg.org>, axboe@...nel.dk,
        dennis@...nel.org, Dennis Zhou <dennisszhou@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...roid.com
Subject: Re: [PATCH 6/6] psi: introduce psi monitor

On Mon, Dec 17, 2018 at 8:22 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Dec 14, 2018 at 09:15:08AM -0800, Suren Baghdasaryan wrote:
> > +ssize_t psi_trigger_parse(char *buf, size_t nbytes, enum psi_res res,
> > +     enum psi_states *state, u32 *threshold_us, u32 *win_sz_us)
> > +{
> > +     bool some;
> > +     bool threshold_pct;
> > +     u32 threshold;
> > +     u32 win_sz;
> > +     char *p;
> > +
> > +     p = strsep(&buf, " ");
> > +     if (p == NULL)
> > +             return -EINVAL;
> > +
> > +     /* parse type */
> > +     if (!strcmp(p, "some"))
> > +             some = true;
> > +     else if (!strcmp(p, "full"))
> > +             some = false;
> > +     else
> > +             return -EINVAL;
> > +
> > +     switch (res) {
> > +     case (PSI_IO):
> > +             *state = some ? PSI_IO_SOME : PSI_IO_FULL;
> > +             break;
> > +     case (PSI_MEM):
> > +             *state = some ? PSI_MEM_SOME : PSI_MEM_FULL;
> > +             break;
> > +     case (PSI_CPU):
> > +             if (!some)
> > +                     return -EINVAL;
> > +             *state = PSI_CPU_SOME;
> > +             break;
> > +     default:
> > +             return -EINVAL;
> > +     }
> > +
> > +     while (isspace(*buf))
> > +             buf++;
> > +
> > +     p = strsep(&buf, "%");
> > +     if (p == NULL)
> > +             return -EINVAL;
> > +
> > +     if (buf == NULL) {
> > +             /* % sign was not found, threshold is specified in us */
> > +             buf = p;
> > +             p = strsep(&buf, " ");
> > +             if (p == NULL)
> > +                     return -EINVAL;
> > +
> > +             threshold_pct = false;
> > +     } else
> > +             threshold_pct = true;
> > +
> > +     /* parse threshold */
> > +     if (kstrtouint(p, 0, &threshold))
> > +             return -EINVAL;
> > +
> > +     while (isspace(*buf))
> > +             buf++;
> > +
> > +     p = strsep(&buf, " ");
> > +     if (p == NULL)
> > +             return -EINVAL;
> > +
> > +     /* Parse window size */
> > +     if (kstrtouint(p, 0, &win_sz))
> > +             return -EINVAL;
> > +
> > +     /* Check window size */
> > +     if (win_sz < PSI_TRIG_MIN_WIN_US || win_sz > PSI_TRIG_MAX_WIN_US)
> > +             return -EINVAL;
> > +
> > +     if (threshold_pct)
> > +             threshold = (threshold * win_sz) / 100;
> > +
> > +     /* Check threshold */
> > +     if (threshold == 0 || threshold > win_sz)
> > +             return -EINVAL;
> > +
> > +     *threshold_us = threshold;
> > +     *win_sz_us = win_sz;
> > +
> > +     return 0;
> > +}
>
> How well has this thing been fuzzed? Custom string parser, yay!

Honestly, not much. Normal cases and some obvious corner cases. Will
check if I can use some fuzzer to get more coverage or will write a
script.
I'm not thrilled about writing a custom parser, so if there is a
better way to handle this please advise.

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