[tip: core/rcu] rculist.h: Add list_tail_rcu()

["tip-bot2 for Madhuparna Bhowmik" <tip-bot2@linutronix.de>]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     afa47fdfa29ffd3324e7b89551d1a6e54ccc042b
Gitweb:        https://git.kernel.org/tip/afa47fdfa29ffd3324e7b89551d1a6e54ccc042b
Author:        Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
AuthorDate:    Mon, 09 Dec 2019 13:20:43 +05:30
Committer:     Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Fri, 10 Jan 2020 14:00:58 -08:00

rculist.h: Add list_tail_rcu()

This patch adds the macro list_tail_rcu() and documents it.

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
[ paulmck: Reword a bit. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/rculist.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 4b7ae1b..9f313e4 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -40,6 +40,16 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  */
 #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))
 
+/**
+ * list_tail_rcu - returns the prev pointer of the head of the list
+ * @head: the head of the list
+ *
+ * Note: This should only be used with the list header, and even then
+ * only if list_del() and similar primitives are not also used on the
+ * list header.
+ */
+#define list_tail_rcu(head)	(*((struct list_head __rcu **)(&(head)->prev)))
+
 /*
  * Check during list traversal that we are within an RCU reader
  */