[PATCH] Fix writeback page range to use exact limits

wait_on_page_writeback_range shouldn't wait for pages beyond the specified
range.  Ideally, the radix-tree-lookup could accept an end_index parameter so
that it doesn't return the extra pages in the first place, but for now we just
add a few extra checks to skip such pages.
Signed-off-by: Suparna Bhattacharya <suparna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/filemap.c

@@ -198,7 +198,8 @@ static int wait_on_page_writeback_range(struct address_space *mapping,
 
 	pagevec_init(&pvec, 0);
 	index = start;
-	while ((nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+	while ((index <= end) &&
+			(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 			PAGECACHE_TAG_WRITEBACK,
 			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
 		unsigned i;
@@ -206,6 +207,10 @@ static int wait_on_page_writeback_range(struct address_space *mapping,
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
 
+			/* until radix tree lookup accepts end_index */
+			if (page->index > end)
+				continue;
+
 			wait_on_page_writeback(page);
 			if (PageError(page))
 				ret = -EIO;