Unkillable linux processes

Hi

I seem to have some unkillable Linux processes...
This is on my AMD Ryzen, the exact same installation on my Broadwell laptop
does not show this behavior.
At the second top output, the three remaining processes' cpu usage is
fluctuating, just as when they are running normally.
Kernel is from one or two days ago with kib's patch that I got the other
day.

root_at_amd:~ # top
  PID USERNAME    THR PRI NICE   SIZE    RES STATE    C   TIME    WCPU
COMMAND
  978 boinc         3 155  i31   129M    64M futex    3   0:52 100.74%
wcgrid_zika_vina_7.
  979 boinc         3 155  i31   112M    47M futex    2   0:56  99.24%
wcgrid_oet1_vina_7.
  980 boinc         2 155  i31   150M    87M CPU3     3   0:46  97.66%
wcgrid_mip1_rosetta
  977 boinc         3 155  i31   109M    43M futex    1   0:56  97.39%
wcgrid_oet1_vina_7.

root_at_amd:~ # service boinc-client stop
Stopping boinc_client.
Waiting for PIDS: 892.
root_at_amd:~ # top

last pid:  1003;  load averages:  3.18,  2.04,
0.94                                          up 0+00:05:31  20:48:06
25 processes:  1 running, 21 sleeping, 3 stopped
CPU:  0.0% user,  0.0% nice, 73.8% system,  0.0% interrupt, 26.2% idle
Mem: 157M Active, 2736K Inact, 300M Wired, 162M Buf, 2907M Free
Swap:

  PID USERNAME    THR PRI NICE   SIZE    RES STATE    C   TIME    WCPU
COMMAND
  977 boinc         2  20  i31   110M    44M STOP     0   3:57 100.00%
wcgrid_oet1_vina_7.
  979 boinc         2  20  i31   113M    47M STOP     0   3:54  97.02%
wcgrid_oet1_vina_7.
  978 boinc         2  20  i31   130M    64M STOP     0   3:50  96.12%
wcgrid_zika_vina_7.

root_at_amd:~ # procstat -ak | grep wcgrid
  977 100162 wcgrid_oet1_vina_7. -                   mi_switch
thread_suspend_switch thread_single exit1 linux_exit_group ia32_syscall
int0x80_syscall_common
  977 100172 wcgrid_oet1_vina_7. -                   witness_checkorder
__mtx_lock_flags linux_sys_futex ia32_syscall int0x80_syscall_common
  978 100163 wcgrid_zika_vina_7. -                   mi_switch
thread_suspend_switch thread_single exit1 linux_exit_group ia32_syscall
int0x80_syscall_common
  978 100174 wcgrid_zika_vina_7. -                   __mtx_lock_flags
futex_put linux_sys_futex ia32_syscall int0x80_syscall_common
  979 100132 wcgrid_oet1_vina_7. -                   mi_switch
thread_suspend_switch thread_single exit1 linux_exit_group ia32_syscall
int0x80_syscall_common
  979 100171 wcgrid_oet1_vina_7. -                   linux_sys_futex
ia32_syscall int0x80_syscall_common