From: Ralph Campbell <rcampb...@nvidia.com>

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.

v3:
[AS]: rename dax_layout_is_idle_page func to dax_page_unused

Signed-off-by: Ralph Campbell <rcampb...@nvidia.com>
Signed-off-by: Alex Sierra <alex.sie...@amd.com>
---
 fs/dax.c            |  4 ++--
 fs/ext4/inode.c     |  5 +----
 fs/xfs/xfs_file.c   |  4 +---
 include/linux/dax.h | 10 ++++++++++
 4 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 26d5dcd2d69e..4820bb511d68 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_page_unused(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_page_unused(page))
                        return page;
        }
        return NULL;
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c173c8405856..9ee00186412f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3972,10 +3972,7 @@ int ext4_break_layouts(struct inode *inode)
                if (!page)
                        return 0;
 
-               error = ___wait_var_event(&page->_refcount,
-                               atomic_read(&page->_refcount) == 1,
-                               TASK_INTERRUPTIBLE, 0, 0,
-                               ext4_wait_dax_page(ei));
+               error = dax_wait_page(ei, page, ext4_wait_dax_page);
        } while (error == 0);
 
        return error;
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 5b0f93f73837..39565fe5f817 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -782,9 +782,7 @@ xfs_break_dax_layouts(
                return 0;
 
        *retry = true;
-       return ___wait_var_event(&page->_refcount,
-                       atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
-                       0, 0, xfs_wait_dax_page(inode));
+       return dax_wait_page(inode, page, xfs_wait_dax_page);
 }
 
 int
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b52f084aa643..8b5da1d60dbc 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -243,6 +243,16 @@ static inline bool dax_mapping(struct address_space 
*mapping)
        return mapping->host && IS_DAX(mapping->host);
 }
 
+static inline bool dax_page_unused(struct page *page)
+{
+       return page_ref_count(page) == 1;
+}
+
+#define dax_wait_page(_inode, _page, _wait_cb)                         \
+       ___wait_var_event(&(_page)->_refcount,                          \
+               dax_page_unused(_page),                         \
+               TASK_INTERRUPTIBLE, 0, 0, _wait_cb(_inode))
+
 #ifdef CONFIG_DEV_DAX_HMEM_DEVICES
 void hmem_register_device(int target_nid, struct resource *r);
 #else
-- 
2.32.0

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