dax: dax_layout_busy_page() warn on !exceptional

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@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

diff --git a/fs/dax.c b/fs/dax.c
index 6411928..897b51e 100644 (file)
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -566,7 +566,8 @@ 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 +579,13 @@ 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++;