There are several places where ZONE_DEVICE struct pages assume a reference
count == 1 means the page is idle and free. Instead of open coding this,
add a helper function to hide this detail.

Signed-off-by: Ralph Campbell <redacted>
---
 fs/dax.c            | 8 ++++----
 fs/ext4/inode.c     | 2 +-
 fs/xfs/xfs_file.c   | 2 +-
 include/linux/dax.h | 5 +++++
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 994ab66a9907..8eddbcc0e149 100644
--- a/fs/dax.c
+++ b/fs/dax.c

@@ -358,7 +358,7 @@ static void dax_disassociate_entry(void *entry, struct address_space *mapping,
        for_each_mapped_pfn(entry, pfn) {
                struct page *page = pfn_to_page(pfn);

-               WARN_ON_ONCE(trunc && page_ref_count(page) > 1);
+               WARN_ON_ONCE(trunc && !dax_layout_is_idle_page(page));
                WARN_ON_ONCE(page->mapping && page->mapping != mapping);
                page->mapping = NULL;
                page->index = 0;

@@ -372,7 +372,7 @@ static struct page *dax_busy_page(void *entry)
        for_each_mapped_pfn(entry, pfn) {
                struct page *page = pfn_to_page(pfn);

-               if (page_ref_count(page) > 1)
+               if (!dax_layout_is_idle_page(page))
                        return page;
        }
        return NULL;

@@ -560,11 +560,11 @@ static void *grab_mapping_entry(struct xa_state *xas,

 /**
  * dax_layout_busy_page - find first pinned page in @mapping
- * @mapping: address space to scan for a page with ref count > 1
+ * @mapping: address space to scan for a page with ref count > 0
  *
  * DAX requires ZONE_DEVICE mapped pages. These pages are never
  * 'onlined' to the page allocator so they are considered idle when
- * page->count == 1. A filesystem uses this interface to determine if
+ * page->count == 0. A filesystem uses this interface to determine if
  * any page in the mapping is busy, i.e. for DMA, or other
  * get_user_pages() usages.
  *

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index bf596467c234..d9f8ad55523a 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c

@@ -3927,7 +3927,7 @@ int ext4_break_layouts(struct inode *inode)
                        return 0;

                error = ___wait_var_event(&page->_refcount,
-                               atomic_read(&page->_refcount) == 1,
+                               dax_layout_is_idle_page(page),
                                TASK_INTERRUPTIBLE, 0, 0,
                                ext4_wait_dax_page(ei));
        } while (error == 0);

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index a29f78a663ca..29ab96541bc1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c

@@ -750,7 +750,7 @@ xfs_break_dax_layouts(

        *retry = true;
        return ___wait_var_event(&page->_refcount,
-                       atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
+                       dax_layout_is_idle_page(page), TASK_INTERRUPTIBLE,
                        0, 0, xfs_wait_dax_page(inode));
 }

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 43b39ab9de1a..3f78ed78d1d6 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h

@@ -238,4 +238,9 @@ static inline bool dax_mapping(struct address_space *mapping)
        return mapping->host && IS_DAX(mapping->host);
 }

+static inline bool dax_layout_is_idle_page(struct page *page)
+{
+       return page_ref_count(page) <= 1;