linux-kernel - Re: [PATCH v2 2/4] mm/hwpoison: check if a subpage of a hugetlb folio is raw HWPOISON

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Message-ID: <20230706220612.GA3768@monkey>
Date:   Thu, 6 Jul 2023 15:06:12 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Jiaqi Yan <jiaqiyan@...gle.com>
Cc:     naoya.horiguchi@....com, songmuchun@...edance.com,
        shy828301@...il.com, linmiaohe@...wei.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, duenwen@...gle.com,
        axelrasmussen@...gle.com, jthoughton@...gle.com
Subject: Re: [PATCH v2 2/4] mm/hwpoison: check if a subpage of a hugetlb
 folio is raw HWPOISON

On 07/06/23 11:25, Jiaqi Yan wrote:
> On Wed, Jul 5, 2023 at 4:57 PM Mike Kravetz <mike.kravetz@...cle.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 = __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.

You can add,

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz