K 10
svn:author
V 4
will
K 8
svn:date
V 27
2013-03-23T16:34:56.773584Z
K 7
svn:log
V 643
ZFS: Fix a panic while unmounting a busy filesystem.

This particular scenario was easily reproduced using a NFS export.  When the
first 'zfs unmount' occurred, it returned EBUSY via this path, while
vflush() had flushed references on the filesystem's root vnode, which in
turn caused its v_interlock to be destroyed.  The next time 'zfs unmount'
was called, vflush() tried to obtain this lock, which caused this panic.

Since vflush() on FreeBSD is a definitive call, there is no need to check
vfsp->vfs_count after it completes.  Simply #ifdef sun this check.

Submitted by:	avg
Reviewed by:	avg
Approved by:	ken (mentor)
MFC after:	1 month

END