linux-kernel - Re: [PATCH v2 1/9] llist: Provide a safe version for llist_for

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Message-ID: <87efz2pmny.fsf@yhuang-dev.intel.com>
Date:   Mon, 13 Feb 2017 15:36:33 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     <peterz@...radead.org>, <mingo@...nel.org>, <neilb@...e.de>,
        <nab@...ux-iscsi.org>, <viro@...iv.linux.org.uk>,
        <ying.huang@...el.com>, <oleg@...hat.com>, <shli@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/9] llist: Provide a safe version for llist_for_each

Byungchul Park <byungchul.park@....com> writes:

> 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.
>
> Signed-off-by: Byungchul Park <byungchul.park@....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..4c508a5 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 type * to use as temporary storage

s/type */&struct llist_node/

> + * @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))
> +

Following the style of other xxx_for_each_safe,

#define llist_for_each_safe(pos, n, node)			\
	for (pos = (node), (pos && (n = pos->next)); pos; pos = n, n = pos->next)

Best Regards,
Huang, Ying

> +/**
>   * 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.