new helper: destroy_unused_super()

Used for disposal of super_block instances that had never been reachable
via any shared data structures.  No need for RCU delay in there, everything
can be called directly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2017-10-11 13:48:55 -04:00
commit 0200894d11