[PATCH 2/4] mm: don't cast ->readpage to filler_t for do_read_cache_page

[Christoph Hellwig <hch@xxxxxx>]

We can just pass a NULL filler and do the right thing inside of
do_read_cache_page based on the NULL parameter.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/pagemap.h |  3 +--
 mm/filemap.c            | 10 ++++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9ec3544baee2..6dd7ec95c778 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -396,8 +396,7 @@ extern int read_cache_pages(struct address_space *mapping,
 static inline struct page *read_mapping_page(struct address_space *mapping,
 				pgoff_t index, void *data)
 {
-	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
-	return read_cache_page(mapping, index, filler, data);
+	return read_cache_page(mapping, index, NULL, data);
 }
 
 /*
diff --git a/mm/filemap.c b/mm/filemap.c
index 6a8048477bc6..3bec6e18b763 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2772,7 +2772,11 @@ static struct page *do_read_cache_page(struct address_space *mapping,
 		}
 
 filler:
-		err = filler(data, page);
+		if (filler)
+			err = filler(data, page);
+		else
+			err = mapping->a_ops->readpage(data, page);
+
 		if (err < 0) {
 			put_page(page);
 			return ERR_PTR(err);
@@ -2884,9 +2888,7 @@ struct page *read_cache_page_gfp(struct address_space *mapping,
 				pgoff_t index,
 				gfp_t gfp)
 {
-	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
-
-	return do_read_cache_page(mapping, index, filler, NULL, gfp);
+	return do_read_cache_page(mapping, index, NULL, NULL, gfp);
 }
 EXPORT_SYMBOL(read_cache_page_gfp);
 
-- 
2.20.1