sleep mutex panic on 5.2.1-RELEASE

Hi,

I have a dual-Xeon system in production (Dell PE2550) that has started to 
randomly lock up, adding debugging fun and WITNESS, I got it to panic 
and pop it into the debugger...

-=-
panic: lock (sleep mutex) pipe mutex not locked 
_at_ /usr/src/sys/kern/sys_pipe.c:854
cpuid = 3;
Debugger("panic")
Stopped at      Debugger+0x55:  xchgl   %ebx,in_Debugger.0
db> trace
Debugger(c085cd10,3,c085f790,f3523b8c,100) at Debugger+0x55
panic(c085f790,c0872db0,c085f140,c085fb54,356) at panic+0x156
witness_unlock(ccae1040,8,c085fb54,356,cc5d36b8) at witness_unlock+0x223
_mtx_unlock_flags(ccae1040,0,c085fb54,356,0) at _mtx_unlock_flags+0x32  
pipe_direct_write(cc5d36b8,f3523c80,c085fb54,372,c0941470) at 
pipe_direct_write+0x511
pipe_write(cc995e9c,f3523c80,cca3f980,0,cc56e500) at pipe_write+0x293
dofilewrite(cc56e500,cc995e9c,1,81ae000,4000) at dofilewrite+0xfb
write(cc56e500,f3523d14,c0878bb8,3ee,3) at write+0x6e
syscall(80e002f,80e002f,bfbf002f,81ae000,4000) at syscall+0x2a0
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (4, FreeBSD ELF32, write), eip = 0x2811b12f, esp = 
0xbfbfdeac, ebp = 0xbfbfdec8 ---
db> reset
cpu_reset called on cpu#3
cpu_reset: Restarting BSP
cpu_reset_proxy: Stopped CPU 3
-=-

Thanks for any info you can provide.

Best Wishes - Peter
-- 
Peter_Losher_at_isc.org | ISC | OpenPGP Key E8048D08 | "The bits must flow"