K 10
svn:author
V 3
kib
K 8
svn:date
V 27
2020-11-26T18:08:42.478457Z
K 7
svn:log
V 498
More careful handling of the mount failure.

- VFS_UNMOUNT() requires vn_start_write() around it [*].
- call VFS_PURGE() before unmount.
- do not destroy mp if cleanup unmount did not succeed.
- set MNTK_UNMOUNT, and indicate forced unmount with MNTK_UNMOUNTF
  for VFS_UNMOUNT() in cleanup.

PR:	251320 [*]
Reported by:	Tong Zhang <ztong0001@gmail.com>
Reviewed by:	markj, mjg
Discussed with:	rmacklem
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D27327

END