deadlock between cpu_stopper & native_flush_tlb_others()->smp_call_function_many()

[Igor Mammedov <imammedo@redhat.com>]

It looks like I hit a deadlock between smp_call_function_many() and
cpu_stopper threads.

Where smp_call_function_many() on CPU1 called from
native_flush_tlb_others() waits on call to be complete on
CPU2 while CPU2 waits on state synchronization in
multi_cpu_stop() which can't be completed until stop work
queued on CPU1 is completed, which can't be done since  CPU1
is busy looping in smp_call_function_many().


CPU1                                       CPU2
stop_machine()
 queue stop work on cpu 1&2

native_flush_tlb_others()
   smp_call_function_many()
      ...
---------------------------------------------------------
                                    cpu_stopper_thread()
                                       multi_cpu_stop()
                                          do {
                                             ...
                                             msdata->state == MULTI_STOP_PREPARE
                                             msdata->active_cpus == 0110
                                             msdata->thread_ack == 1
                                          } while (curstate != MULTI_STOP_EXIT)
                                    waiting until CPU1 ACKs state, i.e. thread_ack == 0
---------------------------------------------------------                                    
      ...
      if (wait) {
         for_cpu(0110) {
           csd_lock_wait(csd);
waiting until call on CPU2 is completed

Are there any suggestions on how to fix this nicely?