kern/47664: Trying to umount a filesystem breaks lstat

[mlelstv%serpens.de@localhost]

>Number:         47664
>Category:       kern
>Synopsis:       Trying to umount a filesystem breaks lstat
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 18 13:15:00 +0000 2013
>Originator:     Michael van Elst
>Release:        NetBSD 6.99.17
>Organization:
organized? me?
>Environment:
        
        
System: NetBSD twitty 6.99.17 NetBSD 6.99.17 (TWITTY) #30: Mon Mar 18 11:54:53 
CET 2013 
mlelstv@pussyfoot:/home/netbsd-current/obj.evbarm/home/netbsd-current/src/sys/arch/evbarm/compile/TWITTY
 evbarm
Architecture: arm
Machine: evbarm
>Description:
Writing to an auto-mounted FFS (FFSv1) filesystem with rsync causes
error messages whenever the automounter tries an umount.

The mounted device is a dk(4) wedge:

/dev/dk7 on /amd/a/dk7 type ffs (local)

rsync shows errors like:

rsync: mkstemp "/amd/a/dk7/netbsd-current/src/usr.bin/mail/.v7.local.c.02069p" 
failed: Device busy (16)

A ktrace reveals that lstat fails:

  2442      1 rsync    CALL  __lstat50(0x6871c,0xbfffc7f4)
  2442      1 rsync    NAMI  "usr.bin/fold"
  2442      1 rsync    RET   __lstat50 -1 errno 16 Device busy

At the same time the kernel sometimes emits an error on console like:

vflushbuf: dirty: vnode @ 0xc1990a54, flags (0x4030<MPSAFE,LOCKSWORK,ONWORKLST>)
        tag VT_UFS(1), type VBLK(3), usecount 325, writecount 0, holdcount 496
        freelisthd 0x0, mount 0xc1834008, data 0xc198e364 lock 0xc1990af8
        tag VT_UFS, ino 33675, on dev 168, 0 flags 0x0, nlink 1
        mode 060640, owner 0, group 5, size 0

>How-To-Repeat:
Automount a local FFS filesystem and ask the automounter to unmount
every few seconds. Then rsync (or probably write somehow) to the
filesytem that is large enough to occur during umount attempts.

>Fix:
        

>Unformatted: