Re: [PATCH v2 1/9] llist: Provide a safe version for llist_for_each
From: Byungchul Park
Date: Mon Feb 13 2017 - 02:44:30 EST
On Mon, Feb 13, 2017 at 03:36:33PM +0800, Huang, Ying wrote:
> Byungchul Park <byungchul.park@xxxxxxx> 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@xxxxxxx>
> > ---
> > 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)
Do you think it should be modified? I think mine is simpler. No?
> 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.