[PATCH] Missing memory barrier in pte_chain_unlock

[Anton Blanchard <anton@samba.org>]

Hi,

On a ppc64 machine running 2.5.28 we were hitting this BUG in
__free_pages_ok:

BUG_ON(page->pte.chain != NULL);

In pte_chain_lock we use test_and_set_bit which implies a memory
barrier. In pte_chain_unlock we use clear_bit which has no memory
barriers so we need to add one.

Anton

===== include/linux/page-flags.h 1.12 vs edited =====
--- 1.12/include/linux/page-flags.h	Wed Jul 17 07:46:30 2002
+++ edited/include/linux/page-flags.h	Thu Jul 25 19:24:52 2002
@@ -249,6 +248,7 @@
 
 static inline void pte_chain_unlock(struct page *page)
 {
+	smp_mb__before_clear_bit();
 	clear_bit(PG_chainlock, &page->flags);
 	preempt_enable();
 }