[NET]: Add missing memory barrier to kfree_skb().

ChangeSet 1.1539.1.4, 2005/02/05 16:56:05-08:00, [email protected]

	[NET]: Add missing memory barrier to kfree_skb().
	
	Also kill kfree_skb_fast(), that is a relic from fast switching
	which was killed off years ago.
	
	The bug is that in the case where we do the atomic_read()
	optimization, we need to make sure that reads of skb state
	later in __kfree_skb() processing (particularly the skb->list
	BUG check) are not reordered to occur before the counter
	read by the cpu.
	
	Thanks to Olaf Kirch and Anton Blanchard for discovering
	and helping fix this bug.
	
	Signed-off-by: Herbert Xu <[email protected]>
	Signed-off-by: David S. Miller <[email protected]>



 skbuff.h |   14 +++++---------
 1 files changed, 5 insertions(+), 9 deletions(-)


diff -Nru a/include/linux/skbuff.h b/include/linux/skbuff.h
--- a/include/linux/skbuff.h	2005-02-09 09:06:14 -08:00
+++ b/include/linux/skbuff.h	2005-02-09 09:06:14 -08:00
@@ -290,15 +290,11 @@
  
 static inline void kfree_skb(struct sk_buff *skb)
 {
-	if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
-		__kfree_skb(skb);
-}
-
-/* Use this if you didn't touch the skb state [for fast switching] */
-static inline void kfree_skb_fast(struct sk_buff *skb)
-{
-	if (atomic_read(&skb->users) == 1 || atomic_dec_and_test(&skb->users))
-		kfree_skbmem(skb);	
+	if (likely(atomic_read(&skb->users) == 1))
+		smp_rmb();
+	else if (likely(!atomic_dec_and_test(&skb->users)))
+		return;
+	__kfree_skb(skb);
 }
 
 /**