[PATCH 1/2] dax: dax_layout_busy_page() warn on !exceptional

[Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

Inodes using DAX should only ever have exceptional entries in their page
caches.  Make this clear by warning if the iteration in
dax_layout_busy_page() ever sees a non-exceptional entry, and by adding a
comment for the pagevec_release() call which only deals with struct page
pointers.

Signed-off-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
---
 fs/dax.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 641192808bb6..4a5e31f8a2d4 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -566,7 +566,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
 			if (index >= end)
 				break;
 
-			if (!radix_tree_exceptional_entry(pvec_ent))
+			if (WARN_ON_ONCE(!radix_tree_exceptional_entry(pvec_ent)))
 				continue;
 
 			xa_lock_irq(&mapping->i_pages);
@@ -578,6 +578,13 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
 			if (page)
 				break;
 		}
+
+		/*
+		 * We don't expect normal struct page entries to exist in our
+		 * tree, but we keep these pagevec calls so that this code is
+		 * consistent with the common pattern for handling pagevecs
+		 * throughout the kernel.
+		 */
 		pagevec_remove_exceptionals(&pvec);
 		pagevec_release(&pvec);
 		index++;
-- 
2.14.4