Subject: Rework btrfs_file_write to only allocate while page locks are held

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 602b63d..15cc9ec 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -541,6 +541,8 @@
 	else
 		ret = submit_bh(WRITE, bh);
 	if (ret == -EOPNOTSUPP) {
+		get_bh(bh);
+		lock_buffer(bh);
 		set_buffer_uptodate(bh);
 		root->fs_info->do_barriers = 0;
 		ret = submit_bh(WRITE, bh);