ovl: initialize OVL_UPPERDATA in ovl_lookup()

ovl: initialize OVL_UPPERDATA in ovl_lookup()

Currently ovl_get_inode() initializes OVL_UPPERDATA flag and for that it
has to call ovl_check_metacopy_xattr() and check if metacopy xattr is
present or not.

yangerkun reported sometimes underlying filesystem might return -EIO and in
that case error handling path does not cleanup properly leading to various
warnings.

Run generic/461 with ext4 upper/lower layer sometimes may trigger the bug
as below(linux 4.19):

[  551.001349] overlayfs: failed to get metacopy (-5)
[  551.003464] overlayfs: failed to get inode (-5)
[  551.004243] overlayfs: cleanup of 'd44/fd51' failed (-5)
[  551.004941] overlayfs: failed to get origin (-5)
[  551.005199] ------------[ cut here ]------------
[  551.006697] WARNING: CPU: 3 PID: 24674 at fs/inode.c:1528 iput+0x33b/0x400
...
[  551.027219] Call Trace:
[  551.027623]  ovl_create_object+0x13f/0x170
[  551.028268]  ovl_create+0x27/0x30
[  551.028799]  path_openat+0x1a35/0x1ea0
[  551.029377]  do_filp_open+0xad/0x160
[  551.029944]  ? vfs_writev+0xe9/0x170
[  551.030499]  ? page_counter_try_charge+0x77/0x120
[  551.031245]  ? __alloc_fd+0x160/0x2a0
[  551.031832]  ? do_sys_open+0x189/0x340
[  551.032417]  ? get_unused_fd_flags+0x34/0x40
[  551.033081]  do_sys_open+0x189/0x340
[  551.033632]  __x64_sys_creat+0x24/0x30
[  551.034219]  do_syscall_64+0xd5/0x430
[  551.034800]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

One solution is to improve error handling and call iget_failed() if error
is encountered.  Amir thinks that this path is little intricate and there
is not real need to check and initialize OVL_UPPERDATA in ovl_get_inode().
Instead caller of ovl_get_inode() can initialize this state.  And this will
avoid double checking of metacopy xattr lookup in ovl_lookup() and
ovl_get_inode().

OVL_UPPERDATA is inode flag.  So I was little concerned that initializing
it outside ovl_get_inode() might have some races.  But this is one way
transition.  That is once a file has been fully copied up, it can't go back
to metacopy file again.  And that seems to help avoid races.  So as of now
I can't see any races w.r.t OVL_UPPERDATA being set wrongly.  So move
settingof OVL_UPPERDATA inside the callers of ovl_get_inode().
ovl_obtain_alias() already does it.  So only two callers now left are
ovl_lookup() and ovl_instantiate().

Reported-by: yangerkun <yangerkun@huawei.com>
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>