nilfs2: wait for discard to finish

nilfs_discard_segment() doesn't wait for completion of discard
requests.  This specifies BLKDEV_IFL_WAIT flag when calling
blkdev_issue_discard() in order to fix the sync failure.

Reported-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Christoph Hellwig <hch@lst.de>

fs/nilfs2/the_nilfs.c

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 6af1c00..4317f17 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -775,6 +775,7 @@
 						   start * sects_per_block,
 						   nblocks * sects_per_block,
 						   GFP_NOFS,
+						   BLKDEV_IFL_WAIT |
 						   BLKDEV_IFL_BARRIER);
 			if (ret < 0)
 				return ret;
@@ -785,7 +786,8 @@
 		ret = blkdev_issue_discard(nilfs->ns_bdev,
 					   start * sects_per_block,
 					   nblocks * sects_per_block,
-					   GFP_NOFS, BLKDEV_IFL_BARRIER);
+					   GFP_NOFS,
+					  BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
 	return ret;
 }