linux-kernel - Re: [kbuild-all] Re: mm/madvise.c:1438:6: warning: Redundant assignment of 'ret' to itself. [selfAssignment]

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Message-ID: <alpine.DEB.2.22.394.2206201253480.2243@hadrien>
Date:   Mon, 20 Jun 2022 12:54:56 -0400 (EDT)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Michal Hocko <mhocko@...e.com>
cc:     Charan Teja Kalla <quic_charante@...cinc.com>,
        kernel test robot <lkp@...el.com>,
        Minchan Kim <minchan@...nel.org>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [kbuild-all] Re: mm/madvise.c:1438:6: warning: Redundant assignment
 of 'ret' to itself. [selfAssignment]



On Mon, 20 Jun 2022, Michal Hocko wrote:

> On Sat 18-06-22 11:25:43, Charan Teja Kalla wrote:
> > Hello Andrew,
> >
> > On 6/18/2022 4:34 AM, kernel test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   4b35035bcf80ddb47c0112c4fbd84a63a2836a18
> > > commit: 5bd009c7c9a9e888077c07535dc0c70aeab242c3 mm: madvise: return correct bytes advised with process_madvise
> > > date:   3 months ago
> > > compiler: mips-linux-gcc (GCC) 11.3.0
> > > reproduce (cppcheck warning):
> > >         # apt-get install cppcheck
> > >         git checkout 5bd009c7c9a9e888077c07535dc0c70aeab242c3
> > >         cppcheck --quiet --enable=style,performance,portability --template=gcc FILE
> > >
> > > If you fix the issue, kindly add following tag where applicable
> > > Reported-by: kernel test robot <lkp@...el.com>
> > >
> > >
> > > cppcheck warnings: (new ones prefixed by >>)
> > >>> mm/madvise.c:1438:6: warning: Redundant assignment of 'ret' to itself. [selfAssignment]
> > >     ret = (total_len - iov_iter_count(&iter)) ? : ret;
> >
> > Other way to avoid this warning is by creating another local variable
> > that holds the total bytes processed. Having another local variable to
> > get rid off some compilation warning doesn't seem proper to me. So,
> > leaving this warning unless you ask me to fix this.
>
> Is this a new warning? I do not see it supported by my gcc 10.x. Do we

cppcheck is a static analysis tool.  It looks like it doesn't have a
proper understanding of ?:

julia

> plan to have it enabled by default? I do not see anything wrong with the
> above code and I think this is not an unusual pattern in the kernel.
> While you could go with
> 	if (rotal_len - iov_iter_count(&iter))
> 		ret = rotal_len - iov_iter_count(&iter);
>
> or do the same with a temporary variable but I am not really sure this would
> add to the readability much.
> --
> Michal Hocko
> SUSE Labs
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