locked vnode / nfs... requires kill -9 in ddb

[John E Hein]

6.2-PRERELEASE from 20061016 RELENG_6 sources.

SMP with 
CPU: Intel(R) Core(TM)2 CPU          6400  @ 2.13GHz (2127.97-MHz 686-class CPU)

GENERIC minus some devices plus:

options IPSEC
options IPSEC_ESP
device  tap
device  vlan
device  hwpmc
options HWPMC_HOOKS
options KDB
options DDB

This also happened a couple times with 6.2-PRERELEASE from 20061004
RELENG_6 sources before I updated a couple days ago.

In userland from a csh session, I used Ctrl-Z to suspend a Bourne
shell script writing to a file through an amd host NFS (tcp v3) mount
back to my own machine.

Sometimes (maybe 5 times out of 20? in the last week) when I do this,
I get a locked vnode problem (see ddb session below) and can't do
anything with the filesystems at all (local or nfs).  Shells hang when
I execute any command (until the suspended 'sh' is killed from ddb).

Interrupts still work, Ctrl-Alt-F# allows switching from X to ttyv*
consoles.

Dropping into ddb allows me to kill the 'sh' with -9 and then
continuing from ddb let's me continue working and things are back to
normal.



KDB: enter: manual escape to debugger
[thread pid 19 tid 100025 ]
Stopped at      0xc05d5bcf = kdb_enter+0x2b:    nop
db> show lockedvnods
Locked vnodes
 
0xc6b7bdd0: tag nfs, type VDIR
    usecount 2, writecount 0, refcount 8 mountedhere 0
    flags (VV_ROOT)
    v_object 0xc9d84108 ref 0 pages 0
     lock type nfs: EXCL (count 1) by thread 0xc8adac00 (pid 50746) with 5 pending
        fileid 8 fsid 0x300ff06

db> ps
  pid  ppid  pgrp   uid   state   wmesg     wchan    cmd
50761  1699 50761     0  S+      nfs      0xc6b7be28 ls
50760  1699 50760     0  S+      nfs      0xc6b7be28 lsof
50759 48969 48935   600  S+      nanslp   0xc088efcc seamonkey-bin
50758 48969 48935   600  S+      nanslp   0xc088efcc seamonkey-bin
50757 50756 50757     0  Ss      nfs      0xc6b7be28 procmail
50756     1   809     0  S       select   0xc0895ba4 sendmail
50751 50750 50751     0  Ss      nfs      0xc6b7be28 procmail
50750     1   809     0  S       select   0xc0895ba4 sendmail
50748 50747  1418   600  SV+     nfs      0xc6b7be28 csh
50747  1418  1418   600  S+      ppwait   0xc8573430 csh
50746 50000 49999   600  T+                          sh
50000  1418 49999   600  T+                          formail
49999  1418 49999   600  T+      pipewr   0xc910f000 cat
 .
 .
db>db> trace 50746
Tracing pid 50746 tid 100231 td 0xc8adac00
sched_switch(c8adac00,0,2) at 0xc05ce0cb = sched_switch+0x173
mi_switch(2,0) at 0xc05c2b0a = mi_switch+0x1ba
thread_suspend_check(1,c079e04c,c8adac00,c9206b80,1,...) at 0xc05c722d = thread_suspend_check+0x191
sleepq_catch_signals(c9206b80) at 0xc05db93f = sleepq_catch_signals+0x103
sleepq_wait_sig(c9206b80) at 0xc05dbd96 = sleepq_wait_sig+0xe
msleep(c9206b80,c08a6a40,153,c0813379,0) at 0xc05c2652 = msleep+0x25a
nfs_reply(c9206b80,0,c8adac00,4,c7ea7100,...) at 0xc06c33ac = nfs_reply+0x244
nfs_request(c6b7bdd0,c6ae2d00,1,c8adac00,c7815280,e8f3488c,e8f34890,e8f34894,c8adac00,e8f348a0) at 0xc06c40a5 = nfs_request+0x3c1
nfs_getattr(e8f348dc) at 0xc06c912b = nfs_getattr+0x11f
VOP_GETATTR_APV(c086c700,e8f348dc) at 0xc07b260c = VOP_GETATTR_APV+0x38
nfsspec_access(e8f34a8c,c6bf7c94,0,e8f349a4,c060ca26,...) at 0xc06cebf1 = nfsspec_access+0x85
nfs_access(e8f34a8c) at 0xc06c8b7a = nfs_access+0x122
VOP_ACCESS_APV(c086c700,e8f34a8c) at 0xc07b25b0 = VOP_ACCESS_APV+0x38
nfs_lookup(e8f34b18) at 0xc06c96ff = nfs_lookup+0xd3
VOP_LOOKUP_APV(c086c700,e8f34b18) at 0xc07b22f7 = VOP_LOOKUP_APV+0x43
lookup(e8f34c00) at 0xc060ee79 = lookup+0x4c1
namei(e8f34c00) at 0xc060e71a = namei+0x39a
kern_stat(c8adac00,806712c,0,e8f34c74) at 0xc061d3cd = kern_stat+0x35
stat(c8adac00,e8f34d04) at 0xc061d37b = stat+0x1b
syscall(3b,3b,3b,1,80670ec,...) at 0xc07a9363 = syscall+0x2bf
Xint0x80_syscall() at 0xc079456f = Xint0x80_syscall+0x1f
--- syscall (188, FreeBSD ELF32, stat), eip = 0x28196477, esp = 0xbfbfdc1c, ebp = 0xbfbfdcb8 ---
db> kill 9 50746
db> c