Re: [PATCH RFC net-next 01/14] rculist_bl: add hlist_bl_for_each_entry_continue_rcu

	Hello,

On Tue, 15 Aug 2023, Paul E. McKenney wrote:

> On Tue, Aug 15, 2023 at 08:30:18PM +0300, Julian Anastasov wrote:
> > Add hlist_bl_for_each_entry_continue_rcu and hlist_bl_next_rcu
> > 
> > Signed-off-by: Julian Anastasov <[email protected]>
> > ---
> >  include/linux/rculist_bl.h | 17 +++++++++++++++++
> >  1 file changed, 17 insertions(+)
> > 
> > diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
> > index 0b952d06eb0b..93a757793d83 100644
> > --- a/include/linux/rculist_bl.h
> > +++ b/include/linux/rculist_bl.h
> > @@ -24,6 +24,10 @@ static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
> >  		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
> >  }
> >  
> > +/* return the next element in an RCU protected list */
> > +#define hlist_bl_next_rcu(node)	\
> > +	(*((struct hlist_bl_node __rcu **)(&(node)->next)))
> > +
> >  /**
> >   * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
> >   * @n: the element to delete from the hash list.
> > @@ -98,4 +102,17 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
> >  		({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
> >  		pos = rcu_dereference_raw(pos->next))
> >  
> > +/**
> > + * hlist_bl_for_each_entry_continue_rcu - iterate over a list continuing after
> > + *   current point
> 
> Please add a comment to the effect that the element continued from
> must have been either: (1) Iterated to within the same RCU read-side
> critical section or (2) Nailed down using some lock, reference count,
> or whatever suffices to keep the continued-from element from being freed
> in the meantime.

	I created 2nd version which has more changes. I'm not sure
what are the desired steps for this patch, should I keep it as part
of my patchset if accepted? Or should I post it separately? Here it
is v2 for comments.

[PATCHv2 RFC] rculist_bl: add hlist_bl_for_each_entry_continue_rcu

Change the old hlist_bl_first_rcu to hlist_bl_first_rcu_dereference
to indicate that it is a RCU dereference.

Add hlist_bl_next_rcu and hlist_bl_first_rcu to use RCU pointers
and use them to fix sparse warnings.

Add hlist_bl_for_each_entry_continue_rcu.

Signed-off-by: Julian Anastasov <[email protected]>
---
 include/linux/rculist_bl.h | 49 +++++++++++++++++++++++++++++++-------
 1 file changed, 40 insertions(+), 9 deletions(-)

diff --git a/include/linux/rculist_bl.h b/include/linux/rculist_bl.h
index 0b952d06eb0b..36363b876e53 100644
--- a/include/linux/rculist_bl.h
+++ b/include/linux/rculist_bl.h
@@ -8,21 +8,31 @@
 #include <linux/list_bl.h>
 #include <linux/rcupdate.h>
 
+/* return the first ptr or next element in an RCU protected list */
+#define hlist_bl_first_rcu(head)	\
+	(*((struct hlist_bl_node __rcu **)(&(head)->first)))
+#define hlist_bl_next_rcu(node)	\
+	(*((struct hlist_bl_node __rcu **)(&(node)->next)))
+
 static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
 					struct hlist_bl_node *n)
 {
 	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
 	LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
 							LIST_BL_LOCKMASK);
-	rcu_assign_pointer(h->first,
+	rcu_assign_pointer(hlist_bl_first_rcu(h),
 		(struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
 }
 
-static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
-{
-	return (struct hlist_bl_node *)
-		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
-}
+#define hlist_bl_first_rcu_dereference(head)				\
+({									\
+	struct hlist_bl_head *__head = (head);				\
+									\
+	(struct hlist_bl_node *)					\
+	((unsigned long)rcu_dereference_check(hlist_bl_first_rcu(__head), \
+					      hlist_bl_is_locked(__head)) & \
+					      ~LIST_BL_LOCKMASK);	\
+})
 
 /**
  * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
@@ -73,7 +83,7 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
 {
 	struct hlist_bl_node *first;
 
-	/* don't need hlist_bl_first_rcu because we're under lock */
+	/* don't need hlist_bl_first_rcu* because we're under lock */
 	first = hlist_bl_first(h);
 
 	n->next = first;
@@ -93,9 +103,30 @@ static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
  *
  */
 #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member)		\
-	for (pos = hlist_bl_first_rcu(head);				\
+	for (pos = hlist_bl_first_rcu_dereference(head);		\
 		pos &&							\
 		({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
-		pos = rcu_dereference_raw(pos->next))
+		pos = rcu_dereference_raw(hlist_bl_next_rcu(pos)))
+
+/**
+ * hlist_bl_for_each_entry_continue_rcu - continue iteration over list of given
+ *   type
+ * @tpos:	the type * to use as a loop cursor.
+ * @pos:	the &struct hlist_bl_node to use as a loop cursor.
+ * @member:	the name of the hlist_bl_node within the struct.
+ *
+ * Continue to iterate over list of given type, continuing after
+ * the current position which must have been in the list when the RCU read
+ * lock was taken.
+ * This would typically require either that you obtained the node from a
+ * previous walk of the list in the same RCU read-side critical section, or
+ * that you held some sort of non-RCU reference (such as a reference count)
+ * to keep the node alive *and* in the list.
+ */
+#define hlist_bl_for_each_entry_continue_rcu(tpos, pos, member)		\
+	for (pos = rcu_dereference_raw(hlist_bl_next_rcu(&(tpos)->member)); \
+	     pos &&							\
+	     ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
+	     pos = rcu_dereference_raw(hlist_bl_next_rcu(pos)))
 
 #endif
-- 
2.41.0


Regards