spin lock sched lock held by 0xc25a8640 for > 5 seconds

I updated bento last night, and it panicked after a few hours with:

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 01
fault virtual address   = 0xe5
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc052e219
stack pointer           = 0x10:0xe00d2c3c
frame pointer           = 0x10:0xe00d2c64
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = resume, IOPL = 0
current process         = 40 (irq29: sym0)
spin lock sched lock held by 0xc25a8640 for > 5 seconds
panic: spin lock held too long
cpuid = 1;
Debugger("panic")

Unfortunately it hangs there instead of breaking to DDB.

The instruction pointer is in:

...
c052e000 t propagate_priority
c052e360 T init_turnstiles
...

I'm currently rebuilding without WITNESS_SKIPSPIN in case this catches it.

Kris