[NET]: Add barriers for dst refcnt.

ChangeSet 1.1539.1.5, 2005/02/05 17:09:11-08:00, [email protected]

	[NET]: Add barriers for dst refcnt.
	
	In light of the recent discussion about sk_buff, I think we need
	the following patch for dst_entry.  This adds a memory barrier
	before dst_release drops the refcnt, and a read memory barrier
	before dst_destroy starts destroying the entry.
	
	Signed-off-by: Herbert Xu <[email protected]>
	Signed-off-by: David S. Miller <[email protected]>



 include/net/dst.h |    4 +++-
 net/core/dst.c    |    9 +++++++--
 2 files changed, 10 insertions(+), 3 deletions(-)


diff -Nru a/include/net/dst.h b/include/net/dst.h
--- a/include/net/dst.h	2005-02-09 09:06:27 -08:00
+++ b/include/net/dst.h	2005-02-09 09:06:27 -08:00
@@ -104,8 +104,10 @@
 static inline
 void dst_release(struct dst_entry * dst)
 {
-	if (dst)
+	if (dst) {
+		smp_mb__before_atomic_dec();
 		atomic_dec(&dst->__refcnt);
+	}
 }
 
 extern void * dst_alloc(struct dst_ops * ops);
diff -Nru a/net/core/dst.c b/net/core/dst.c
--- a/net/core/dst.c	2005-02-09 09:06:27 -08:00
+++ b/net/core/dst.c	2005-02-09 09:06:27 -08:00
@@ -142,8 +142,13 @@
 
 void dst_destroy(struct dst_entry * dst)
 {
-	struct neighbour *neigh = dst->neighbour;
-	struct hh_cache *hh = dst->hh;
+	struct neighbour *neigh;
+	struct hh_cache *hh;
+
+	smp_rmb();
+
+	neigh = dst->neighbour;
+	hh = dst->hh;
 
 	dst->hh = NULL;
 	if (hh && atomic_dec_and_test(&hh->hh_refcnt))