[PATCH][xenial] UBUNTU: SAUCE: fs: Allow psuedo-fs superblocks to be reused in other namespaces

[Seth Forshee]

For psuedo filesystems it's not critical that s_user_ns match the
user namespace where the superblock is being mounted, and this
check is currently breaking cgroup namespaces. Skip the check
for psuedo filesystems.

Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
---
 fs/super.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index 732bffa..1f2bfd7 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -471,7 +471,8 @@ retry:
 		hlist_for_each_entry(old, &type->fs_supers, s_instances) {
 			if (!test(old, data))
 				continue;
-			if (user_ns != old->s_user_ns) {
+			if ((type->fs_flags & FS_REQUIRES_DEV) &&
+			    user_ns != old->s_user_ns) {
 				spin_unlock(&sb_lock);
 				return ERR_PTR(-EBUSY);
 			}
-- 
1.9.1