This actually checks that writeback is needed or in progress.

Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
---
 mm/filemap.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d9572593e5c7..29f503ffd70b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -618,10 +618,13 @@ int filemap_fdatawait_keep_errors(struct address_space 
*mapping)
 }
 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
+/* Returns true if writeback might be needed or already in progress. */
 static bool mapping_needs_writeback(struct address_space *mapping)
 {
-       return (!dax_mapping(mapping) && mapping->nrpages) ||
-           (dax_mapping(mapping) && mapping->nrexceptional);
+       if (dax_mapping(mapping))
+               return mapping->nrexceptional;
+
+       return mapping->nrpages;
 }
 
 int filemap_write_and_wait(struct address_space *mapping)

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