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From:   Jiaqi Yan <jiaqiyan@google.com>
Date:   Thu, 6 Jul 2023 18:27:11 -0700
Message-ID: <CACw3F51gnG7vUowL-Q4_DBRL=DAHsr7hvcBMT90OF_dLQLoDaQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/4] mm/hwpoison: check if a subpage of a hugetlb folio
 is raw HWPOISON
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     naoya.horiguchi@nec.com, songmuchun@bytedance.com,
        shy828301@gmail.com, linmiaohe@huawei.com,
        akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, duenwen@google.com,
        axelrasmussen@google.com, jthoughton@google.com
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On Thu, Jul 6, 2023 at 3:06=E2=80=AFPM Mike Kravetz <mike.kravetz@oracle.co=
m> wrote:
>
> On 07/06/23 11:25, Jiaqi Yan wrote:
> > On Wed, Jul 5, 2023 at 4:57=E2=80=AFPM Mike Kravetz <mike.kravetz@oracl=
e.com> wrote:
> > > On 06/23/23 16:40, Jiaqi Yan wrote:
> > > >
> > > > +bool is_raw_hwp_subpage(struct folio *folio, struct page *subpage)
> > > > +{
> > > > +     bool ret;
> > > > +
> > > > +     spin_lock_irq(&hugetlb_lock);
> > > > +     ret =3D __is_raw_hwp_subpage(folio, subpage);
> > > > +     spin_unlock_irq(&hugetlb_lock);
> > >
> > > Can you describe what races the hugetlb_lock prevents here?
> >
> > I think we should sync here with __get_huge_page_for_hwpoison, who
> > iterates and inserts an entry to raw_hwp_list. llist itself doesn't
> > ensure insertion is synchronized with iterating from
> > __is_raw_hwp_subpage.
> >
>
> Ok, makes sense.  And, since this is only called in the file read patch
> when we encounter a PageHWPoison(page), the overhead of the lock cycles
> is not of concern.

Yes, thanks for pointing this out, (which I forgot), as
is_raw_hwp_subpage() is after PageHWPoison check in
hugetlbfs_read_iter. I think both this and the reason why holding the
lock is worth mentioning in the commit msg.


>
> You can add,
>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> --
> Mike Kravetz