linux-kernel - Re: gcc-8: mm/swapfile.c:863:40: error: array subscript 1 is above array bounds of 'struct list

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Message-ID: <CACePvbVJab1QNv35jepKYVdXV1Brnn=sTwBx7Vs5fr-93jDQvQ@mail.gmail.com>
Date: Tue, 20 Aug 2024 01:51:41 -0700
From: Chris Li <chrisl@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Kairui Song <ryncsn@...il.com>, Naresh Kamboju <naresh.kamboju@...aro.org>, 
	linux-mm <linux-mm@...ck.org>, open list <linux-kernel@...r.kernel.org>, 
	lkft-triage@...ts.linaro.org, Linux Regressions <regressions@...ts.linux.dev>, 
	Barry Song <21cnbao@...il.com>, "Huang, Ying" <ying.huang@...el.com>, 
	Hugh Dickins <hughd@...gle.com>, Kalesh Singh <kaleshsingh@...gle.com>, 
	Ryan Roberts <ryan.roberts@....com>, Anders Roxell <anders.roxell@...aro.org>
Subject: Re: gcc-8: mm/swapfile.c:863:40: error: array subscript 1 is above
 array bounds of 'struct list_head[1]' [-Werror=array-bounds]

On Mon, Aug 19, 2024 at 10:05 PM Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> On Mon, 19 Aug 2024 19:44:25 +0800 Kairui Song <ryncsn@...il.com> wrote:
>
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -836,7 +836,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
> >               goto done;
> >
> >       /* Order 0 stealing from higher order */
> > -     for (int o = 1; o < PMD_ORDER; o++) {
> > +     for (int o = 1; o < SWAP_NR_ORDERS; o++) {
> >               /*
> >                * Clusters here have at least one usable slots and can't fail order 0
> >                * allocation, but reclaim may drop si->lock and race with another user.
>
> OK, I got that landed in the right place, but...
>
> The definition of `o' within the for statement isn't typical kernel
> style - I'm surprised we didn't get a warning for this - maybe things
> have changed when I wasn't looking.

Noted.

I did use the checkpatch.pl and fixed all the warnings before I sent
the patch out.
The checkpatch.pl script did not complain about this. Sure I can stay
away from it.
BTW, I did  a search on the kernel tree:
$ rg 'for \(int' | wc -l
970
$
It seems pretty common in the kernel tree now.

>
> Also, this code makes no attempt to honor our "The preferred limit on
> the length of a single line is 80 columns" objective.  There's just no
> reason for comment blocks to violate this.

I was wondering why the checkpatch.pl did not catch this, is there any
config for checkpatch.pl I should apply?

I typically invoke:

./scripts/checkpatch.pl -g HEAD

Let me know if there is a better way to invoke checkpatch.pl to give
more warnings.

Chris