overlay: Regression test for deadlock on directory ioctl

overlay: Regression test for deadlock on directory ioctl

Overlayfs added the ability to set inode flags (e.g. chattr +i) in
kernel 5.10 by commit 61536bed2149 ("ovl: support [S|G]ETFLAGS and
FS[S|G]ETXATTR ioctls for directories").
Icenowy Zheng reported [1] a regression in that commit that causes
a deadlock when setting inode flags on lower dir.

The regression was fixed by commit b854cc659dcb ("ovl: avoid deadlock
on directory ioctl") and applied to kernel 5.10.15.

[1] https://lore.kernel.org/linux-unionfs/20210101201230.768653-1-icenowy@aosc.io/

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>