From cdbf8897cb09b7baf2b8a7e78051a35a872b01d5 Mon Sep 17 00:00:00 2001
From: Ross Zwisler <ross.zwisler@linux.intel.com>
Date: Sun, 29 Jul 2018 16:59:16 -0400
Subject: [PATCH] dax: dax_layout_busy_page() warn on !exceptional
Git-commit: cdbf8897cb09b7baf2b8a7e78051a35a872b01d5
Patch-mainline: v4.19-rc1
References: bsc#1104888

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>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/dax.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/dax.c
+++ b/fs/dax.c
@@ -570,7 +570,8 @@ struct page *dax_layout_busy_page(struct
 			if (index >= end)
 				break;
 
-			if (!radix_tree_exceptional_entry(pvec_ent))
+			if (WARN_ON_ONCE(
+			     !radix_tree_exceptional_entry(pvec_ent)))
 				continue;
 
 			spin_lock_irq(&mapping->tree_lock);
@@ -582,6 +583,13 @@ struct page *dax_layout_busy_page(struct
 			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++;