Just to be clear, you stated:

crash -d1 shows me

crash: get_netdump_panic_task: crashing_cpu: 1
crash: get_netdump_panic_task: failed
crash: get_active_set_panic_task: failed

and I presumed:
 

Now, since after the "crash: get_active_set_panic_task: failed"
message, there are no more error messages, so panic_search()
must have determined that the idle thread (swapper) on cpu 0 was
in fact the running task that took the sysrq.

But, are there any other error messages after the
"get_active_set_panic_task: failed"?  Like for
example:

  crash: panic_search: failed (via foreach bt)
  crash: get_panic_context: panic task not found

or did you see:

  crash: panic_search: ffffffff80335340 (via foreach bt)

Thanks,
  Dave