Unkillable process in STOP state

[Slawa Olhovchenkov]

I have amd64, STABLE r288167.

root at edge09:/home/admin # procstat -k -k 627
  PID    TID COMM             TDNAME           KSTACK                       
  627 100167 tcpkali.new      -                mi_switch+0xe1 thread_suspend_switch+0x170 thread_single+0x4e5 exit1+0xbe sys_sys_exit+0xe amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100172 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100173 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100174 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100175 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100178 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 100180 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 102207 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 102208 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 102209 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
  627 102211 tcpkali.new      -                mi_switch+0xe1 sleepq_timedwait_sig+0x8b _sleep+0x238 kern_kevent+0x401 sys_kevent+0x12a amd64_syscall+0x357 Xfast_syscall+0xfb 
root at edge09:/home/admin # procstat -t 627
  PID    TID COMM             TDNAME           CPU  PRI STATE   WCHAN    
  627 100167 tcpkali.new      -                 10  120 stop    -         
  627 100172 tcpkali.new      -                  3  152 stop    -         
  627 100173 tcpkali.new      -                  5  152 stop    -         
  627 100174 tcpkali.new      -                  3  152 stop    -         
  627 100175 tcpkali.new      -                  2  149 stop    -         
  627 100178 tcpkali.new      -                  5  152 stop    -         
  627 100180 tcpkali.new      -                  2  132 stop    -         
  627 102207 tcpkali.new      -                  5  136 stop    -         
  627 102208 tcpkali.new      -                  3  152 stop    -         
  627 102209 tcpkali.new      -                  5  139 stop    -         
  627 102211 tcpkali.new      -                  1  120 stop    -         

kill -STOP don't have effect.
gdb can't be attached.