Received-SPF: pass (google.com: domain of linux-kernel+bounces-199323-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <20240603140745.83880-1-ioworker0@gmail.com> <Zl3Wjh9_aGY8Xxm7@casper.infradead.org>
In-Reply-To: <Zl3Wjh9_aGY8Xxm7@casper.infradead.org>
From: Lance Yang <ioworker0@gmail.com>
Date: Mon, 3 Jun 2024 22:55:37 +0800
Message-ID: <CAK1f24kKkX8Ed-MGUJbEhJFSUa2CLpo+H-f3ijVBnqFHRHdA3Q@mail.gmail.com>
Subject: Re: [PATCH v2 1/1] mm/mlock: implement folio_mlock_step() using folio_pte_batch()
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, david@redhat.com, 
	21cnbao@gmail.com, baolin.wang@linux.alibaba.com, ziy@nvidia.com, 
	fengwei.yin@intel.com, ying.huang@intel.com, libang.li@antgroup.com, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Mon, Jun 3, 2024 at 10:43=E2=80=AFPM Matthew Wilcox <willy@infradead.org=
> wrote:
>
> On Mon, Jun 03, 2024 at 10:07:45PM +0800, Lance Yang wrote:
> > +++ b/mm/mlock.c
> > @@ -307,26 +307,15 @@ void munlock_folio(struct folio *folio)
> >  static inline unsigned int folio_mlock_step(struct folio *folio,
> >               pte_t *pte, unsigned long addr, unsigned long end)
> >  {
> > -     unsigned int count, i, nr =3D folio_nr_pages(folio);
> > -     unsigned long pfn =3D folio_pfn(folio);
> > +     const fpb_t fpb_flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRT=
Y;
> > +     unsigned int count =3D (end - addr) >> PAGE_SHIFT;
>
> This is a pre-existing bug, but ... what happens if you're on a 64-bit
> system and you mlock() a range that is exactly 2^44 bytes?  Seems to me
> that count becomes 0.  Why not use an unsigned long here and avoid the
> problem entirely?

Good catch! Thanks for pointing that out!
Let's use an unsigned long here instead to avoid the problem entirely :)

Thanks,
Lance

>
> folio_pte_batch() also needs to take an unsigned long max_nr in that
> case, because you aren't restricting it to folio_nr_pages().
>