Since commit 8e1f385104ac ("kill task_struct->thread_group") remove
the thread_group, we will encounter below issue.
(gdb) lx-ps
TASK PID COMM
0xffff800086503340 0 swapper/0
Python Exception <class 'gdb.error'>: There is no member named thread_group.
Error occurred in Python: There is no member named thread_group.
We use signal->thread_head to iterate all threads instead.
Fixes: 8e1f385104ac ("kill task_struct->thread_group")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx>