From jlayton@redhat.com  Wed Mar 21 11:42:20 2018
From: Jeff Layton <jlayton@redhat.com>
Subject: dax: set errors in mapping when writeback fails
Git-commit: 819ec6b91d5ba1ca313066a306461774eff6b567
Patch-mainline: v4.13-rc1
References: bsc#1086149 bsc#1086285

Jan Kara's description for this patch is much better than mine, so I'm
quoting it verbatim here:

DAX currently doesn't set errors in the mapping when cache flushing
fails in dax_writeback_mapping_range(). Since this function can get
called only from fsync(2) or sync(2), this is actually as good as it can
currently get since we correctly propagate the error up from
dax_writeback_mapping_range() to filemap_fdatawrite()

However, in the future better writeback error handling will enable us to
properly report these errors on fsync(2) even if there are multiple file
descriptors open against the file or if sync(2) gets called before
fsync(2). So convert DAX to using standard error reporting through the
mapping.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-and-tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Acked-by: Jeff Mahoney <jeffm@suse.com>
---
 fs/dax.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index c22eaf162f95..441280e15d5b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -856,8 +856,10 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 
 			ret = dax_writeback_one(bdev, dax_dev, mapping,
 					indices[i], pvec.pages[i]);
-			if (ret < 0)
+			if (ret < 0) {
+				mapping_set_error(mapping, ret);
 				goto out;
+			}
 		}
 		start_index = indices[pvec.nr - 1] + 1;
 	}