From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 21 Jun 2013 16:51:13 +0000 (-0400)
Subject: rculist: ensure atomic updates of next pointers
X-Git-Tag: v0.8.0~59
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=db757a4e5c7ecba45a79dc9c15090cb3deb659b5;p=userspace-rcu.git

rculist: ensure atomic updates of next pointers

in cds_list_add_rcu, use rcu_assign_pointer to update head->next
atomically and provide the memory barrier before publishing head->next.
Notice that we don't need the wmb() prior to store to prev, because RCU
traversals only go forward, and thus only use "next".

in cds_list_del_rcu, use CMM_STORE_SHARED() to store to elem->prev->next
atomically.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/urcu/rculist.h b/urcu/rculist.h
index ab88226..1fd2df3 100644
--- a/urcu/rculist.h
+++ b/urcu/rculist.h
@@ -35,9 +35,8 @@ void cds_list_add_rcu(struct cds_list_head *newp, struct cds_list_head *head)
 {
 	newp->next = head->next;
 	newp->prev = head;
-	cmm_smp_wmb();
 	head->next->prev = newp;
-	head->next = newp;
+	rcu_assign_pointer(head->next, newp);
 }
 
 /* Add new element at the tail of the list. */
@@ -70,7 +69,7 @@ static inline
 void cds_list_del_rcu(struct cds_list_head *elem)
 {
 	elem->next->prev = elem->prev;
-	elem->prev->next = elem->next;
+	CMM_STORE_SHARED(elem->prev->next, elem->next);
 }
 
 /*