dax: fix regression in dax_writeback_mapping_range()

commit 354ae7432ee8 ("dax: add tracepoints to
dax_writeback_mapping_range()") in the -next tree, which appears in
next-20170310, inadvertently changed dax_writeback_mapping_range() so that
it could end up returning a positive value: the number of bytes flushed,
as returned by dax_writeback_one().  This was incorrect.  This function
either needs to return a negative error value, or zero on success.

This change was causing xfstest failures, as reported by Xiong:

https://lkml.org/lkml/2017/3/13/1220

With this fix applied to next-20170310, all the test failures reported by
Xiong (generic/075 generic/112 generic/127 generic/231 generic/263) are
resolved.

Link: http://lkml.kernel.org/r/20170314215358.31451-1-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Xiong Zhou <xzhou@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/dax.c b/fs/dax.c
index 5dd7b286c091..7cf2686761e2 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -891,7 +891,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 out:
 	put_dax(dax_dev);
 	trace_dax_writeback_range_done(inode, start_index, end_index);
-	return ret;
+	return (ret < 0 ? ret : 0);
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);