Hi Dave,
I also came across the same problem,
tt->refresh_hash_table is set to refresh_hlist_task_table_v2(),
after executing the function the tt->current is set to 0 (zero).
(gdb) p *tt
$3 = {current = 0x0, context_array = 0x8194e4f0, refresh_task_table =
0x800b1380 <refresh_hlist_task_table_v2>, flags = 1608, task_start = 0,
task_end = 0, task_local = 0x8179bda0,
  max_tasks = 154, nr_threads = 70, running_tasks = 2, retries = 0,
panicmsg = 0, panic_processor = 0, idle_threads = {3384520, 12953368, 0
<repeats 62 times>}, panic_threads = {
    0 <repeats 64 times>}, panic_ksp = {0 <repeats 64 times>}, active_set =
{3384520, 32872136, 0 <repeats 62 times>}, hardirq_ctx = {0 <repeats 64
times>}, hardirq_tasks = {
    0 <repeats 64 times>}, softirq_ctx = {0 <repeats 64 times>},
softirq_tasks = {0 <repeats 64 times>}, panic_task = 0, this_task = 0,
pidhash_len = 1024, pidhash_addr = 4037248,
  last_task_read = 12953368, last_thread_info_read = 13058048, last_mm_read
= 0, task_struct = 0x815eb8e0 "", thread_info = 0x81623ad0 "",
mm_struct =
0x8175e420 ""}
(gdb)
Regards
                                                                            
 Hariharan T.S.                                                             
 System Software Engineer,                                                  
 zSeries - Red Hat Enterprise Linux,                                        
 India Software Lab - IBM Systems & Technology Group,                       
 Embassy Golf Links Business Park, Bangalore, INDIA                         
 Direct +91-80-4177-7545                                                    
 e-mail: hariharan.ts(a)in.ibm.com                                            
 India Software Lab                                                         
                                                                            
Jeff Layton wrote:
      I was trying to run crash against a live rawhide kernel and am
      getting
      some errors when I try to start it: