linux-kernel - Re: [RESEND PATCH] llist: Provide a safe version for llist_for

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Message-ID: <20170518020344.GE28017@X58A-UD3R>
Date:   Thu, 18 May 2017 11:03:44 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@....com,
        ying.huang@...el.com
Subject: Re: [RESEND PATCH] llist: Provide a safe version for llist_for_each

On Fri, May 12, 2017 at 09:36:56AM +0900, Byungchul Park wrote:
> Sometimes we have to dereference next field of llist node before entering
> loop becasue the node might be deleted or the next field might be
> modified within the loop. So this adds the safe version of llist_for_each,
> that is, llist_for_each_safe.

+cc ying.huang@...el.com

> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> Reviewed-by: "Huang, Ying" <ying.huang@...el.com>
> ---
>  include/linux/llist.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/include/linux/llist.h b/include/linux/llist.h
> index fd4ca0b..b90c9f2 100644
> --- a/include/linux/llist.h
> +++ b/include/linux/llist.h
> @@ -105,6 +105,25 @@ static inline void init_llist_head(struct llist_head *list)
>  	for ((pos) = (node); pos; (pos) = (pos)->next)
>  
>  /**
> + * llist_for_each_safe - iterate over some deleted entries of a lock-less list
> + *			 safe against removal of list entry
> + * @pos:	the &struct llist_node to use as a loop cursor
> + * @n:		another &struct llist_node to use as temporary storage
> + * @node:	the first entry of deleted list entries
> + *
> + * In general, some entries of the lock-less list can be traversed
> + * safely only after being deleted from list, so start with an entry
> + * instead of list head.
> + *
> + * If being used on entries deleted from lock-less list directly, the
> + * traverse order is from the newest to the oldest added entry.  If
> + * you want to traverse from the oldest to the newest, you must
> + * reverse the order by yourself before traversing.
> + */
> +#define llist_for_each_safe(pos, n, node)			\
> +	for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n))
> +
> +/**
>   * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
>   * @pos:	the type * to use as a loop cursor.
>   * @node:	the fist entry of deleted list entries.
> -- 
> 1.9.1