xfs_init_new_inode ignores the init_xattrs parameter for filesystems
that do not have ATTR enabled.  As a result, the first init_xattrs file
to be created by the kernel will not have an attr fork created to store
acls.  Storing that first acl will add ATTR to the superblock flags, so
subsequent files will be created with attr forks.  The overhead of this
is so small that chances are that nobody has noticed this behavior.

However, this is disastrous on a filesystem with parent pointers because
it requires that a new linkable file /must/ have a pre-existing attr
fork, and the parent pointers code uses init_xattrs to create that fork.
The preproduction version of mkfs.xfs used to set this, but the V5 sb
verifier only requires ATTR2, not ATTR.  There is no guard for
filesystems with (PARENT && !ATTR).

It turns out that I misunderstood the two flags -- ATTR means that we at
some point created an attr fork to store xattrs in a file; ATTR2
apparently means only that inodes have dynamic fork offsets or that the
filesystem was mounted with the "attr2" option.

Fixes: 2442ee15 ("xfs: eager inode attr fork init needs attr feature awareness")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>