Check for PageSwapCache after looking up swap page.

The page migration code may change a swap pte to point to a different page
under lock_page().

If that happens then the vm must retry the lookup operation in the swap
space to find the correct page number. There are a couple of locations
in the VM where a lock_page() is done on a swap page. In these locations
we need to check afterwards if the page was migrated. If the page was migrated
the it no longer has the PageSwapCache bit set.

Signed-off-by: Hirokazu Takahashi <taka@valinux.co.jp>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Christoph Lameter <clameter@@sgi.com>

Index: linux-2.6.14-rc5-mm1/mm/memory.c
===================================================================
--- linux-2.6.14-rc5-mm1.orig/mm/memory.c	2005-10-24 10:27:12.000000000 -0700
+++ linux-2.6.14-rc5-mm1/mm/memory.c	2005-10-28 16:09:11.000000000 -0700
@@ -1665,6 +1665,7 @@ static int do_swap_page(struct mm_struct
 		goto out;
 
 	entry = pte_to_swp_entry(orig_pte);
+again:
 	page = lookup_swap_cache(entry);
 	if (!page) {
  		swapin_readahead(entry, address, vma);
@@ -1688,6 +1689,12 @@ static int do_swap_page(struct mm_struct
 
 	mark_page_accessed(page);
 	lock_page(page);
+	if (!PageSwapCache(page)) {
+		/* Page migration has occured */
+		unlock_page(page);
+		page_cache_release(page);
+		goto again;
+	}
 
 	/*
 	 * Back out if somebody else already faulted in this pte.
Index: linux-2.6.14-rc5-mm1/mm/shmem.c
===================================================================
--- linux-2.6.14-rc5-mm1.orig/mm/shmem.c	2005-10-24 10:27:12.000000000 -0700
+++ linux-2.6.14-rc5-mm1/mm/shmem.c	2005-10-28 16:08:20.000000000 -0700
@@ -1013,6 +1013,14 @@ repeat:
 			page_cache_release(swappage);
 			goto repeat;
 		}
+		if (!PageSwapCache(swappage)) {
+			/* Page migration has occured */
+			shmem_swp_unmap(entry);
+			spin_unlock(&info->lock);
+			unlock_page(swappage);
+			page_cache_release(swappage);
+			goto repeat;
+		}
 		if (PageWriteback(swappage)) {
 			shmem_swp_unmap(entry);
 			spin_unlock(&info->lock);
Index: linux-2.6.14-rc5-mm1/mm/swapfile.c
===================================================================
--- linux-2.6.14-rc5-mm1.orig/mm/swapfile.c	2005-10-24 10:27:36.000000000 -0700
+++ linux-2.6.14-rc5-mm1/mm/swapfile.c	2005-10-28 16:08:20.000000000 -0700
@@ -624,6 +624,7 @@ static int try_to_unuse(unsigned int typ
 		 */
 		swap_map = &si->swap_map[i];
 		entry = swp_entry(type, i);
+again:
 		page = read_swap_cache_async(entry, NULL, 0);
 		if (!page) {
 			/*
@@ -658,6 +659,12 @@ static int try_to_unuse(unsigned int typ
 		wait_on_page_locked(page);
 		wait_on_page_writeback(page);
 		lock_page(page);
+		if (!PageSwapCache(page)) {
+			/* Page migration has occured */
+			unlock_page(page);
+			page_cache_release(page);
+			goto again;
+		}
 		wait_on_page_writeback(page);
 
 		/*