[PATCH 4.9 30/39] fs/dax.c: fix inefficiency in dax_writeback_mapping_range()

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@xxxxxxx>

commit 1eb643d02b21412e603b42cdd96010a2ac31c05f upstream.

dax_writeback_mapping_range() fails to update iteration index when
searching radix tree for entries needing cache flushing.  Thus each
pagevec worth of entries is searched starting from the start which is
inefficient and prone to livelocks.  Update index properly.

Link: http://lkml.kernel.org/r/20170619124531.21491-1-jack@xxxxxxx
Fixes: 9973c98ecfda3 ("dax: add support for fsync/sync")
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/dax.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/dax.c
+++ b/fs/dax.c
@@ -785,6 +785,7 @@ int dax_writeback_mapping_range(struct a
 			if (ret < 0)
 				return ret;
 		}
+		start_index = indices[pvec.nr - 1] + 1;
 	}
 	return 0;
 }