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

[Jiaqi Yan <jiaqiyan@google.com>]

On Thu, Jul 6, 2023 at 3:06 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 07/06/23 11:25, Jiaqi Yan wrote:
> > On Wed, Jul 5, 2023 at 4:57 PM Mike Kravetz <mike.kravetz@oracle.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.

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