fstest generic/696 failure on ext4 fs with quotas+idmap

[Luis Henriques <lhenriques@suse.de>]

Hi!

The fstest generic/696 (and 697) fail on ext4 when the filesystem is
created with quota support (-O quota).  It's really easy to reproduce, and
it fails when doing the idmapped tests (setgid_create_umask_idmapped() and
setgid_create_umask_idmapped_in_userns()).

The failure happens when the test does an openat() with O_TMPFILE:

  ext4_tmpfile()
    __ext4_new_inode()
      dquot_initialize()
        dqget()

and at this point the error occurs:

	if (!qid_has_mapping(sb->s_user_ns, qid))
		return ERR_PTR(-EINVAL);

qid is '-1', which is invalid, but I'm failing to understand if it should
really be invalid or if dqget() should handle this invalid qid some other
way.  Earlier, __ext4_new_inode() called inode_init_owner(), which indeed
sets inode->i_uid with '-1'.

I've been trying to figure it out, but it's very tricky to follow all the
details, so I decided to ask here and see if anyone has any idea.  Is this
a known issue?  Maybe the issue is with the test itself, and not with
ext4, quota or idmapped code.

Cheers,
-- 
Luís