Re: [PATCH v2 2/3] llist: add a safe version of llist_for_each_entry

[Huang Ying]

On Mon, 2012-12-10 at 18:24 +0100, Roger Pau Monne wrote:
> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>
> ---
>  include/linux/llist.h |   27 +++++++++++++++++++++++++++
>  1 files changed, 27 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/llist.h b/include/linux/llist.h
> index a5199f6..f611cd8 100644
> --- a/include/linux/llist.h
> +++ b/include/linux/llist.h
> @@ -125,6 +125,33 @@ static inline void init_llist_head(struct llist_head *list)
>  	     (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
>  
>  /**
> + * llist_for_each_entry_safe - safely iterate over some deleted entries of
> + *                             lock-less list of given type
> + * @pos:	the type * to use as a loop cursor.
> + * @n:		the &struct llist_node to use as a temporary loop cursor
> + * @node:	the fist entry of deleted list entries.
> + * @member:	the name of the llist_node with the struct.
> + *
> + * In general, some entries of the lock-less list can be traversed
> + * safely only after being removed 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.
> + *
> + * n is used to store a reference to the next item llist_node, so
> + * pos can be freed while iterating.
> + */
> +#define llist_for_each_entry_safe(pos, n, node, member)		\
> +	for ((pos) = llist_entry((node), typeof(*(pos)), member),	\
> +	     (n) = (pos)->member.next;					\

If node == NULL, (pos)->member.next will trigger NULL reference.

Best Regards,
Huang Ying

> +	     &(pos)->member != NULL;					\
> +	     (pos) = llist_entry(n, typeof(*(pos)), member),		\
> +	     (n) = (&(pos)->member != NULL) ? (pos)->member.next : NULL)
> +
> +/**
>   * llist_empty - tests whether a lock-less list is empty
>   * @head:	the list to test
>   *


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