From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Tue, 13 Jul 2010 15:57:30 +0000 (-0400)
Subject: RCU lock-free stack: don't hold read lock across retry
X-Git-Tag: v0.4.7~21
X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=commitdiff_plain;h=2e6c64324e20fc31ccb6af3717e8d6b040869ed6

RCU lock-free stack: don't hold read lock across retry

Be nicer to grace-periods.

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

diff --git a/urcu/rculfstack.h b/urcu/rculfstack.h
index 6df6d72..48f6297 100644
--- a/urcu/rculfstack.h
+++ b/urcu/rculfstack.h
@@ -43,10 +43,11 @@ void rcu_lfs_init(struct rcu_lfs_stack *s)
 
 void rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
 {
-	rcu_read_lock();
 	for (;;) {
-		struct rcu_lfs_node *head = rcu_dereference(s->head);
+		struct rcu_lfs_node *head;
 
+		rcu_read_lock();
+		head = rcu_dereference(s->head);
 		node->next = head;
 		/*
 		 * uatomic_cmpxchg() implicit memory barrier orders earlier
@@ -57,6 +58,7 @@ void rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
 			return;
 		} else {
 			/* Failure to prepend. Retry. */
+			rcu_read_unlock();
 			continue;
 		}
 	}
@@ -70,10 +72,11 @@ void rcu_lfs_push(struct rcu_lfs_stack *s, struct rcu_lfs_node *node)
 struct rcu_lfs_node *
 rcu_lfs_pop(struct rcu_lfs_stack *s)
 {
-	rcu_read_lock();
 	for (;;) {
-		struct rcu_lfs_node *head = rcu_dereference(s->head);
+		struct rcu_lfs_node *head;
 
+		rcu_read_lock();
+		head = rcu_dereference(s->head);
 		if (head) {
 			struct rcu_lfs_node *next = rcu_dereference(head->next);
 
@@ -82,6 +85,7 @@ rcu_lfs_pop(struct rcu_lfs_stack *s)
 				return head;
 			} else {
 				/* Concurrent modification. Retry. */
+				rcu_read_unlock();
 				continue;
 			}
 		} else {