fsync: giving up on dirty, umount -f fails

Hi,

I am archiving some old disks and while trying to umount [-f] them I am 
getting errors and I basically cannot get rid of the mount anymore 
without rebooting.  This is on a HEAD from mid-end-August (around 
r351518M).

Given there is a lot of work going on at the moment to deal with 
“disks dropping out by error” and not to panic I was just wondering 
if this is something to address as well?   Somehow umount -f should be 
able to succeed (in the future)?


fsync: giving up on dirty (error = 5) 
g_vfs_done():da0s2g[READ(offset=4666441728, length=16384)]error = 5
0xfffff803533b81e0: tag devfs, type VCHR
     usecount 1, writecount 0, refcount 1661 rdev 0xfffff8015372a800
     flags (VI_ACTIVE)
     v_object 0xfffff80365537c00 ref 0 pages 8340 cleanbuf 1561 dirtybuf 
97
     lock type devfs: EXCL by thread 0xfffff80006a57000 (pid 26526, 
umount, tid 100091)
         dev da0s2g


/bz