Re: ZFS panic: System call unlink returning with 1 locks held

In the last episode (Jul 21), Thierry Herbelot said:
> with a recent -current -built yesterday), I just got a panic while 
> rebuilding -j4 the world and portupgrading firefox.
>
> the machine is pretty much memory limited (only 320 MB of RAM), with
> two CPUs, running a straight GENERIC kernel, including WITNESS and
> INVARIANTS.
[..]
> the panic message is :
> 
> panic: System call unlink returning with 1 locks held
> cpuid = 0
> KDB: enter: panic
> [thread pid 42789 tid 100102 ]
> Stopped at      kdb_enter+0x32: leave
> db> where
> Tracing pid 42789 tid 100102 td 0xc2ce3200
> kdb_enter(c0a92bc5,0,c0ac0a31,d5457c8c,0,...) at kdb_enter+0x32
> panic(c0ac0a31,c0a98f5c,1,c0a98f5c,c0b3f030,...) at panic+0x124
> syscall(d5457d38) at syscall+0x46e
> Xint0x80_syscall() at Xint0x80_syscall+0x20

I've been seeing this, as late as on a Jul 24 kernel.  Happened once
during the cleandir stage of a buildworld, and few more times when the
system was relatively idle (although it is an mrtg server so lots of
files are constantly created and rm'd).  My system is i386 with 1GB of
RAM, has a ZFS root, and is SMP.  I've also gotten a similar "System
call rename returning with 1 locks held" panic.  Is there any way to
find out what lock is being held?  I've got a couple crashdumps.

(kgdb) (kgdb) #0  doadump () at pcpu.h:195
#1  0xc05e4032 in boot (howto=260) at ../../../kern/kern_shutdown.c:409
#2  0xc05e43b9 in panic (fmt=0xc0845a19 "System call %s returning with %d locks held") at ../../../kern/kern_shutdown.c:563
#3  0xc07c203b in syscall (frame=0xe76dfd38) at ../../../i386/i386/trap.c:1060
#4  0xc07a6a00 in Xint0x80_syscall () at ../../../i386/i386/exception.s:196

-- 
	Dan Nelson
	dnelson_at_allantgroup.com