[PATCH 4.6 203/203] ovl: warn instead of error if d_type is not supported

[Greg Kroah-Hartman]

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vivek Goyal <vgoyal@xxxxxxxxxx>

commit e7c0b5991dd1be7b6f6dc2b54a15a0f47b64b007 upstream.

overlay needs underlying fs to support d_type. Recently I put in a
patch in to detect this condition and started failing mount if
underlying fs did not support d_type.

But this breaks existing configurations over kernel upgrade. Those who
are running docker (partially broken configuration) with xfs not
supporting d_type, are surprised that after kernel upgrade docker does
not run anymore.

https://github.com/docker/docker/issues/22937#issuecomment-229881315

So instead of erroring out, detect broken configuration and warn
about it. This should allow existing docker setups to continue
working after kernel upgrade.

Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Fixes: 45aebeaf4f67 ("ovl: Ensure upper filesystem supports d_type")
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/overlayfs/super.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1072,11 +1072,13 @@ static int ovl_fill_super(struct super_b
 			if (err < 0)
 				goto out_put_workdir;
 
-			if (!err) {
-				pr_err("overlayfs: upper fs needs to support d_type.\n");
-				err = -EINVAL;
-				goto out_put_workdir;
-			}
+			/*
+			 * We allowed this configuration and don't want to
+			 * break users over kernel upgrade. So warn instead
+			 * of erroring out.
+			 */
+			if (!err)
+				pr_warn("overlayfs: upper fs needs to support d_type.\n");
 		}
 	}