[4.9-stable PATCH 02/11] fs/dax.c: fix inefficiency in dax_writeback_mapping_range()

[Dan Williams]

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>
---
 fs/dax.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/dax.c b/fs/dax.c
index 800748f10b3d..71f87d74afe1 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -785,6 +785,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 			if (ret < 0)
 				return ret;
 		}
+		start_index = indices[pvec.nr - 1] + 1;
 	}
 	return 0;
 }