linux-kernel - Re: [PATCH v2 1/4] mm/hwpoison: delete all entries before traversal in __folio_free_raw

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Date:   Thu, 6 Jul 2023 11:11:37 -0700
From:   Jiaqi Yan <jiaqiyan@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.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 1/4] mm/hwpoison: delete all entries before traversal
 in __folio_free_raw_hwp

On Wed, Jul 5, 2023 at 4:36 PM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 06/23/23 16:40, Jiaqi Yan wrote:
> > Traversal on llist (e.g. llist_for_each_safe) is only safe AFTER entries
> > are deleted from the llist.
> >
> > llist_del_all are lock free with itself. folio_clear_hugetlb_hwpoison()s
> > from __update_and_free_hugetlb_folio and memory_failure won't need
> > explicit locking when freeing the raw_hwp_list.
> >
> > Signed-off-by: Jiaqi Yan <jiaqiyan@...gle.com>
> > ---
> >  mm/memory-failure.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
>
> After updating the reason for patch in commit message as suggested by Naoya,

Thank you both Mike and Naoya! I will add the explanation in the next version.

>
> Acked-by: Mike Kravetz <mike.kravetz@...cle.com>
>
> --
> Mike Kravetz
>
> >
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index 004a02f44271..c415c3c462a3 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -1825,12 +1825,11 @@ static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
> >
> >  static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
> >  {
> > -     struct llist_head *head;
> > -     struct llist_node *t, *tnode;
> > +     struct llist_node *t, *tnode, *head;
> >       unsigned long count = 0;
> >
> > -     head = raw_hwp_list_head(folio);
> > -     llist_for_each_safe(tnode, t, head->first) {
> > +     head = llist_del_all(raw_hwp_list_head(folio));
> > +     llist_for_each_safe(tnode, t, head) {
> >               struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> >
> >               if (move_flag)
> > @@ -1840,7 +1839,6 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
> >               kfree(p);
> >               count++;
> >       }
> > -     llist_del_all(head);
> >       return count;
> >  }
> >
> > --
> > 2.41.0.162.gfafddb0af9-goog
> >