linux-kernel - Re: [PATCH v1] PM: runtime: Avoid device usage count underflows

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Message-ID: <CAJZ5v0h-hB918OxUjHQCypyR8JKNEV8FxR7LRYaraoq+Mazfhw@mail.gmail.com>
Date:   Mon, 11 Apr 2022 20:07:25 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v1] PM: runtime: Avoid device usage count underflows

On Mon, Apr 11, 2022 at 6:53 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Apr 11, 2022 at 6:17 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > On Mon, Apr 11, 2022 at 5:09 PM Andy Shevchenko
> > <andy.shevchenko@...il.com> wrote:
> > > On Wed, Apr 6, 2022 at 11:49 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> ...
>
> > > > +               retval = rpm_drop_usage_count(dev);
> > > > +               if (retval > 0) {
> > > >                         trace_rpm_usage_rcuidle(dev, rpmflags);
> > > >                         return 0;
> > > > +               } else if (retval < 0) {
> > > > +                       return retval;
> > > >                 }
> > >
> > > Can be written in a form
> > >
> > >                if (retval < 0)
> > >                        return retval;
> > >                if (retval > 0) {
> > >                        trace_rpm_usage_rcuidle(dev, rpmflags);
> > >                        return 0;
> > >                }
> > >
> >
> > I know.
> >
> > And why would it be better?
>
> Depends on the perception:

Well, exactly.

> a) less characters to parse (no 'else');

But to me, with the "else" it is clear that the conditionals are
related to each other which is not so clear otherwise at first sight.
YMMV

> b) checking for errors first, which seems more or less standard pattern.

So the checks can be reversed no problem, but this is such a minor point ,,,