PLEASE TEST: IPI deadlock avoidance patch

[andy at bradfieldprichard.com.au]

>
> Could you set the following sysctl:
>
>   debug.kdb.stop_cpus=0
>

(hand typed - sorry about the wrapping)

panic: APIC: Previous IPI is stuck
cpuid = 0;
KDB: enter: panic
[thread 100161]
Stopped at      kdb_enter+0x30: leave
db> where
kdb_enter(c08b3ec5,0,c08d2917,d6a33c90,c1f689a0) at kdb_enter+0x30
panic(c08d2917,2,d6a33cb0,3,8) at panic+0x15a
lapic_ipi_vectored(fb,4,d6a33d44,d6a33d44,c19d4280)
 at lapic_ipi_vectored+0xa3
ipi_selected(e,fb,d6a33d44,d6a33cec,c084a0ea) at ipi_selected+0x43
forward_hardclock(d6a33d44,0,c08d44e3,bd,c1b35580)
 at forward_hardclock+0x49
clkintr(d6a33d44,6,d6a33d40,c0846be0,0) at clkintr+0xba
intr_execute_handlers(c0954fc0,d6a33d44,28562640,d6a33d3c,1)
 at intr_execute_handlers+0xbb
atpic_handle_intr(0) at atpic_handle_intr+0xcf
Xatpic_intr0() at Xatpic_intr0+0x20
--- interrupt, eip = 0x81a6ddb, esp = 0xbfbfe270, epb = 0xbfbfe278 ---
db>

-andyf