Should rather just use the non-zeroing usercopy here, but the APIs for it
don't seem to be very consistent.

Signed-off-by: Nick Piggin <npiggin@suse.de>

 mm/filemap.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -2200,7 +2200,15 @@ generic_file_buffered_write(struct kiocb
 			bytes = copied;
 
 			lock_page(page);
-			if (unlikely(!page->mapping)) {
+			/*
+			 * Can't handle the page going uptodate here, because
+			 * that means we would use non-atomic usercopies, which
+			 * zero out the tail of the page, which can cause
+			 * zeroes to become transiently visible. We could just
+			 * use a non-zeroing copy, but the APIs aren't too
+			 * consistent.
+			 */
+			if (unlikely(!page->mapping || PageUptodate(page))) {
 				unlock_page(page);
 				page_cache_release(page);
 				page_cache_release(src_page);