Below is the  warning dump from 2.16.18-rt3 built for ARM/XScale
(ixp4xx) and .config attached.

Note that the kernel continues on and boots to a shell with no other
problems.

Kevin

khelper/58[CPU#0]: BUG in trace_hardirqs_on at
/home/khilman/work/kernel/ixp4xx/dev/kernel/lockdep.c:1805
[<c00282dc>] (dump_stack+0x0/0x28) from [<c0036f50>] (__WARN_ON+0x5c/0x78)
[<c0036ef4>] (__WARN_ON+0x0/0x78) from [<c00534c8>]
(trace_hardirqs_on+0x100/0x184)
 r8 = 00000000  r7 = 00000000  r6 = C0031F94  r5 = C417AA60
 r4 = C41A5440
[<c00533c8>] (trace_hardirqs_on+0x0/0x184) from [<c0031f94>]
(schedule_tail+0xc0/0x110)
 r6 = 00008040  r5 = C417AA60  r4 = C0236720
[<c0031ed4>] (schedule_tail+0x0/0x110) from [<c0023fe4>]
(ret_from_fork+0x4/0x40)
 r6 = 00000000  r5 = 00000000  r4 = 00000000
---------------------------
| preempt count: 00000002 ]
| 2-level deep critical section nesting:
----------------------------------------
.. [<c0024fac>] .... alloc_thread_info+0x1c/0x84
.....[<c00337e4>] ..   ( <= copy_process+0x80/0x123c)
.. [<c01e8960>] .... __spin_lock_irqsave+0x34/0x68
.....[<c0036f20>] ..   ( <= __WARN_ON+0x2c/0x78)