Hang in NFS client operation

Since 2005-04-09 (*), my (-current) box sometimes hang at NFS client
operation (usually CVS update from readonly NFS mounted repository.
Server is 5.3R).

Is there something I can help debugging about this issue?

-----
db> ps
  pid   proc     uid  ppid  pgrp  flag   stat  wmesg    wchan  cmd
 7778 c3b73e00  103  7776  7767 0004000 [SLPQ nfsreq 0xc3d87e80][SLP] cvs
...
db> trace 7778
Tracing pid 7778 tid 100124 td 0xc3b6b300
sched_switch(c3b6b300,0,1) at sched_switch+0x14f
mi_switch(1,0,c3b6b300,1,c3b6b300) at mi_switch+0x1ba
sleepq_switch(c3d87e80) at sleepq_switch+0x133
sleepq_wait(c3d87e80,0,c3bc5298,0,c3d87e80) at sleepq_wait+0xb
msleep(c3d87e80,c0721a60,53,c06c28fc,0) at msleep+0x356
nfs_reply(c3d87e80,0,f,0,c3b6b300) at nfs_reply+0x23c
nfs_request(c4d69aa0,c3eb1200,3,c3b6b300,c3bf0d80) at nfs_request+0x3c1
nfs_lookup(ecf93bd8) at nfs_lookup+0x2d8
VOP_LOOKUP_APV(c06f8ba0,ecf93bd8) at VOP_LOOKUP_APV+0x38
lookup(ecf93c68,ecf93c14,0,c3b6b300,ecf93c90) at lookup+0x431
namei(ecf93c68,c3bf0d80,c3dd8e00,80c3080,0) at namei+0x396
kern_access(c3b6b300,80c3080,0,4,ecf93d30) at kern_access+0x6a
access(c3b6b300,ecf93d04,2,2d7,286) at access+0x15
syscall(3b,bfbf003b,bfbf003b,80c3080,80de8c0) at syscall+0x2b3
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (33, FreeBSD ELF32, access), eip = 0x282e6bc7, esp = 0xbfbfe47c, ebp = 0xbfbfe498 ---


-----
(*) I tried to find actual commit by using binary search:
    <http://lists.freebsd.org/pipermail/cvs-src/2005-April/044449.html>

>  Modified files:
>    sys/kern             vfs_lookup.c 
>  Log:
>   - If we vrele() a dvp while the child is locked we can potentially
>    deadlock
>     when vrele() acquires the directory lock in the wrong order.  Fix
>    this
>     via the following changes:
>  ...


-- 
Jun Kuriyama <kuriyama_at_imgsrc.co.jp> // IMG SRC, Inc.
             <kuriyama_at_FreeBSD.org> // FreeBSD Project