linux-kernel - Re: [PATCH 2/2] x86/resctrl: Use appropriate API for strings terminated by newline

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Message-ID: <CAHp75VdoVxDaBYtiH8D_0DLKcwP7AAS2M7XoyrDj7LAv8cOoDA@mail.gmail.com>
Date:   Fri, 3 Apr 2020 10:27:59 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>, kuo-lang.tseng@...el.com,
        Ingo Molnar <mingo@...hat.com>, babu.moger@....com,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86/resctrl: Use appropriate API for strings
 terminated by newline

On Fri, Apr 3, 2020 at 12:54 AM Reinette Chatre
<reinette.chatre@...el.com> wrote:
> On 4/2/2020 6:06 AM, Andy Shevchenko wrote:
> > On Wed, Apr 01, 2020 at 11:30:48AM -0700, Reinette Chatre wrote:

...

> >> @@ -1412,11 +1412,11 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
> >>      struct rdtgroup *rdtgrp;
> >>      enum rdtgrp_mode mode;
> >>      int ret = 0;
> >> +    int user_m;
> >>
>
> >
> > ...and forgot to mention this...
> >
> >       int user_m;
> >       int ret;
> >
>
> >
> >>      /* Valid input requires a trailing newline */
> >>      if (nbytes == 0 || buf[nbytes - 1] != '\n')
> >>              return -EINVAL;
> >> -    buf[nbytes - 1] = '\0';
> >
> > The above test is not needed and comment now is misleading.
> > WRT nbytes I believe that kernel fs code checks for that.

This module provides it's own kernfs_ops...

> If nbytes is 0 it is still passed to this function. You are correct that
> those tests are not needed though (if nbytes is 0 then
> sysfs_match_string() will not find a match and return EINVAL via that path).
>
> Thank you for catching this. I'll remove those unnecessary checks.

...which means that nbytes == 0 is a valid check. Please keep it
there. It will protect from unnecessary locking and loading CPU for
nothing.

-- 
With Best Regards,
Andy Shevchenko