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

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Message-ID: <20230630145217.GA2213127@ik1-406-35019.vs.sakura.ne.jp>
Date:   Fri, 30 Jun 2023 23:52:17 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Jiaqi Yan <jiaqiyan@...gle.com>
Cc:     mike.kravetz@...cle.com, 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 Fri, Jun 23, 2023 at 04:40:12PM +0000, 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>

(Sorry if stupid question...) folio_set_hugetlb_hwpoison() also calls
llist_for_each_safe() but it still traverses the list without calling
llist_del_all().  This convention applies only when removing item(s)?

Thanks,
Naoya Horiguchi

> ---
>  mm/memory-failure.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> 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
> 
> 
>